Two-Keyed Lock

Dr. Petrov: This is most unnerving, Captain. The whole reason for having two keys is so that no one man...may...
Captain Ramius: May what, Doctor?
Dr. Petrov: ...May arm the missiles, Captain. Perhaps I should hold the other key—
Captain Ramius: Mmm, thank you, Doctor. That will be all.

— The Hunt for Red October^note After Ramius takes and keeps the nuclear missile launch key from the ship's dead political officer, whom he secretly killed, meaning that he is now in possession of both launch keys.

Certain locks require two or more people to unlock them simultaneously. The idea is that even if someone malicious got hold of one key, they'd still need to get hold of the second key. And even if they managed to do that, they'd still need to be able to turn all the keys at once, which are usually placed too far apart for one person to do so on their own. Maybe it's the keys to the world's destruction or the kingdom's treasure, but whatever it is, it's so important that you know it must be good... or really bad.

Common in military settings and very much Truth in Television with Nuclear Weapons. An implementation of the more general military concept of "Two Person Control" (TPC).

A variation seen in video games, especially ones with co-op play, is a stock puzzle that requires two characters to activate triggers in different places at the same time to complete an objective.

May sometimes be played for laughs, where the thing being protected by the two keyed lock turns out to be something mundane, or even silly. Not to be confused with Double Unlock, which is about enabling new game features.

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Examples:

Anime & Manga

• Goldion Crusher in GaoGaiGar uses this method, a step up from the Hammer, which just required one key. It's unsurprising as to why, given that the thing destroyed an entire star the one time it was ever used.
• Neon Genesis Evangelion:
  • In episode 13, an Angel infiltrates NERV's computer system and Gendo tries to be Genre Savvy.
    Gendo: Shut down the I/O system.
    [Hyuga and Aoba insert keys into their respective slots]
    Hyuga: Three! Two! One! [keys are turned]
    [beat]
    Hyuga: WE CAN'T SHUT IT DOWN!!!
  • Then a few minutes later, Maya and Ritsuko do this to hack into the Angel through Casper while Casper is being hacked by the Angel in turn. They enter the final command simultaneously and it works, killing the Angel and disarming the MAGI's self-destruct sequence a single second before it could blow the entire base to kingdom come.
  • In fact, this is how the MAGI self-destruct works: the three cores vote among themselves. Starting or cancelling the sequence requires unanimity of all three; cheating is impossible since any attempts at one core hacking another are immediately discovered. If two disagree and the third is undecided, they'll ask the human crew.
• The Cyclops system in Mobile Suit Gundam SEED was so inhumane (and probably expensive, considering that it was one-shot only) that it required at least five top Earth Alliance generals' keys to turn on. This was reduced to only two in the anime, and the system was set up so that it was possible to have one person to turn both keys as long as he had them. The keys were kept on two separate generals, however.
• Lyrical Nanoha:
  • The Arc-en-Ciel superweapon in Magical Girl Lyrical Nanoha A's requires two officers to activate, and special permission from the top brass for them to even carry the keys for it in the first place. Given the destruction it's capable of, this is well-warranted.
  • The final Power Limiter placed upon Hayate Yagami in Magical Girl Lyrical Nanoha StrikerS had to be removed simultaneously by Admiral Chrono Harlaown and Knight Carim, making it one even though they didn't have to be physically present near Hayate at the time.
• The mechanism for detonating KaibaCorp Island in Yu-Gi-Oh! requires two key cards to activate.
• In Yu-Gi-Oh! GX, Duel Academy Island is the home of the three Sacred Beasts (essentially evil versions of the Egyptian God Cards), which are sealed away beneath the academy. Unlocking them requires seven keys which are being targeted by the Shadow Riders; to protect the keys, Chancellor Shepard entrusts them to Jaden Yuki and his friends.
• In El-Hazard: The Magnificent World, the Kingdom of Roshstaria's Eye of God superweapon requires its two sovereigns to activate: first and second princesses Rune and Fatora Venus. The absence of the later drives much of the plot following the main character's arrival in El Hazard.

Comic Books

• Irredeemable. After Plutonian returns and seems intent on killing everyone on Earth, the representatives of China and Japan approach the acting President of the United States with news of a weapon that will defeat the supervillain, but will also kill billions through slow radiation poisoning. It requires all three of them to activate, not only for the usual reasons but also so they share responsibility for this heinous act.
• The lab where the Extremis samples were kept in Iron Man: Extremis. This was a key plot point.
• In Paperinik New Adventures, Morgan Fairfax had the remote of his earthquake-generating system with two keys, of which he kept one himself and the other was given to Mary Ann Flagstarr, his bodyguard (who didn't know his plan) without telling her what it was, so Paperinik or others couldn't stop him by force but he was still able to access the key in case he found it necessary. Just in case, he still had a very complex set of codes in place, something that got handy when Flagstarr realized Paperinik was telling the truth and our heroes realized the twin necklaces were the needed keys.

Fan Works

• The entrance to the white key chamber in The Keys Stand Alone: The Soft World is opened by two people placing their hands in two separate hand-shaped indentations, one on the floor, one on the ceiling.

Films — Animation

• Used to shut down honey production in Bee Movie.
• In Inside Out, Riley's father's emotions need to turn two keys (held by his Fear and Disgust) to fire the foot (i.e. tell Riley to go to her room).
• In My Little Pony: Equestria Girls – Forgotten Friendship, Celestia and Luna open the Bookcase Passage by pulling on a pair of books. Each one uses her own telekinesis to move the book with her respective cutie mark on the spine. Since it should be trivially easy for either of them to do both at the same time, this hints that there is a security system requiring the two alicorns to work in tandem to get access to the restricted section of the library.
• Scooby-Doo! and KISS: Rock and Roll Mystery: Four-keyed example. The MacGuffin the witch wants is kept inside a box that cannot be opened unless Demon, Starchild, Spaceman and Catman open it together.

Films — Live-Action

• Bellman & True (and Same Story, Different Names The Real McCoy) has a two-key lock to enable or disable the elevator. During a five minute phase for the bank break in, they spend most of the time trying to figure out which of the keys open the elevator, in addition to discovering the order in which the keys are turned.
• Coupled with Borrowed Biometric Bypass in Charlie's Angels (2000), where entering a corporation's computer vault requires the fingerprints of one director and the iris scan of another. Inside the vault is another set of buttons that have to be pushed simultaneously. Natalie solves this one by using her foot to reach the second button.
• The Cloverfield Paradox. Two keys are required to fire the particle accelerator. When Jensen tries to stop the process, she has to kill Monk and take his key before going to kill Schmidt, who holds the other.
• Terminator 2: Judgment Day has a two-keyed lock to access the vault where the arm and chip of the previous film's Terminator is kept.
• WarGames, to control a nuclear launch. One officer gets held at gunpoint for refusing to turn his key when ordered, even though it was just a drill. That inspires NORAD to turn over launch control to an AI and leads to the main plot of the movie.
  Silo Officer #2: (aiming gun) Sir, we are at launch! Turn your key, sir!
  Silo Officer #1: (softly) I'm sorry...
  Silo Officer #2: (cocks gun) Turn your key, sir!
• Played with in Under Siege 2: Dark Territory, where it was two passwords on computer keyboards that needed to be entered simultaneously.
• Superman III, to boot up a computer system located at a Webscoe subsidiary in Smallville called WheatKing; although the two keys in question needed to be inserted simultaneously, not turned.
• The nuclear missile locks in The Hunt for Red October had one of these. Although we never see the locks themselves, we see Captain Ramius taking possession of both keys — which, as the doctor points out, sort of defeats the point. The movie plays with the idea that Ramius has gone mad and intends to start WW3, but in the novel this idea is rejected as five officers are needed to carry out a launch. It also stated that in the event of the political officer's death, the captain was supposed to take charge of his key. There were probably other standing orders as to who inherits the other keys in the event of any of the other officers with launch keys dying on a voyage as well. A two key (two combination in the book) system was also used on a safe in the submarine that contained the mission orders and code books. Moreover, while the movie version plays up that Captain Ramius took both launch keys as if he could single-handedly activate the missiles, the locks are intentionally positioned far apart enough in the room that it is physically impossible for one man to turn both keys simultaneously.
• In Dr. Strangelove, the pilot, bombardier and electronic warfare officer each have to operate the first and second safety switches to arm the bombs.
• Sunshine has a high-tech version; instead of two keys, to override the Master Computer they need the voice patterns from two different crew members. At one point the computer starts turning the spaceship's heat shield towards the sun because a fire has broken out in their oxygen garden, endangering the ship. Unfortunately the captain is EVA on the heat shield, putting his life in danger. One crewman tries to override the computer. A second refuses to do, because their mission (to save the entire human race) is more important than one man's life. A higher ranking officer then backs up the first. The captain then overrides him in turn.
• The Librarian has this, as two security guards are needed to activate the elevator leading down to the actual Library.
  Flynn: Hey, don't nuclear launch codes require this?
  Charlene: Who do you think they got it from?
• The Lost in Space movie required two keys to activate the hyperdrive.
• Crimson Tide: Two keys needed to unlock the missile launch controls. The XO refuses the captain's orders to unlock the controls because they lost communications before the launch order was confirmed as protocol demands. Mutiny ensues.
  • One might notice that this is exactly why there are two keys.
  • The captain was in fact acting on legitimate launch orders, and the XO was refusing those orders due to the possibility they had received orders to cancel the launch. The real villains of the film were the (unseen) President and Secretary of Defense, who issued nuclear launch orders with the intention of rescinding them if the situation changed. There are no take-backs in thermonuclear warfare.
  • Aside from the captain and XO having their own arming keys, the captain's safe has additional keys that needed to be passed out to other crew members during launch preparations. The missile launching switch itself was also located in the Missile Control Compartment, behind a multi-door safe; only the weapons officer (played by Viggo Mortensen) had the combinations to the locks.
  • In addition, when the launch order comes in, two officers are required to authenticate it. One reads a random series of letters printed on the order while the other one reads a series of letters from an authenticator kept aboard ship. If both sequences match, the order is authentic.
• James Bond:
  • GoldenEye had this for the titular weapon as well, defeated by simply having two villains working together. Interestingly, this was replicated in the secret underground base as well.
  • No Time to Die: SPECTRE raids a secret MI6 laboratory and demands access to one of the biovaults, which requires two scientists. The moment the two are identified, the others are shot dead, then when the weapon they are after has been removed, one of the scientists is killed and the other taken with them.
• Star Trek:
  • The USS Enterprise self-destruct sequence needed spoken confirmation from three senior officers to trigger in Star Trek III: The Search for Spock.
  • That destruct sequence is taken verbatim from the infamously anvilicious TOS episode "Let That Be Your Last Battlefield". Twenty years later, they still hadn't changed the codes, to the point where Chekov has to declare himself "acting Science Officer" rather than his normal position as chief of Security.
  • In TNG, it's often the Captain and Executive Officer, so the "two senior officers" may be in lieu of the XO in the event that they are unavailable. The Enterprise-E was slated to self-destruct on confirmation from Worf and Crusher, since Riker was unavailable at the time.
• In The First Great Train Robbery, the safes holding the gold need a total of four keys to be opened.
• In Amazing Grace and Chuck, the explanation of why this is in place in the nuclear missile control room (and why the men stationed in such a secure area are armed) is part of what terrifies Chuck when he's touring the silo.
• Combined with No OSHA Compliance in Hulk as the locks are close enough for David Banner to activate the Self-Destruct Mechanism after stealing both keys.
• Godzilla (2014). A nuclear weapon on the deck of a naval vessel is armed via this trope, which along with the spinning cogs, countdown clock, and the keylocks being about three feet apart is presumably for Rule of Drama rather than realism.
• Captain America: Civil War opens with a Hydra scientist entering a research lab in Siberia. Just to get inside the front door involves this trope, as there are two guards standing on either side of the huge door to open it for him.
• The Soldier. In the ICBM base, the keys are only to open the glass panels covering two red-handled levers which perform the same function.
• In The Film of the Book of The Dead Zone, John Smith has a vision of Gregory Stillson as President of the United States. Stillson is hot to launch a nuclear strike at the Soviet Union, but to activate the Nuclear Football, he needs a general's handprint-scan in addition to his own. Stillson tells the general, "Put your hand on that pad, or I'll cut it off and do it myself!"
• In Hostile Waters, launching the K-219's missiles requires two keys, one held by Captain Britanov and the other held by Security Officer Pshenishny. The launch procedure is not shown, but the security surrounding the keys is - each key is kept locked in a safe in its holder's cabin, with the safes requiring both a second key and a combination to open. The two key holders are also required to inspect each other's keys periodically, verifying in the presence of another officer that they are "in good order and secure."
• The 2023 film Last Sentinel has the two key version for a Doomsday Device, but it's useless as one man can still set off the device himself, while holding down a Dead Man's Switch that prevents anyone from rushing him. When the commander of the sea fort where the device is kept decides to keep both keys to himself, it doesn't reassure the rest of his crew.
• Steel Rain. After the ruler of North Korea is wounded in a coup, what looks like a smart watch is removed from his wrist but when South Korean intelligence try to examine the watch they find it's heavily encoded. Meanwhile the coup leader is trying to activate North Korea's nuclear arsenal. He's handed the code generator, but is told there's a second code generator that their Great Leader always carried with him. So he has military hackers break the codes of the individual nukes and is able to launch one of them that way. However the protagonist pretends he's stolen the watch and brings it back to him; it's been replaced with a Tracking Device enabling an airstrike to be called in on the coup leader's secret bunker.
• K-19: The Widowmaker twice sees the crew go through their missile launch procedures.^*Once during a dockside exercise, once when launching an unarmed test missile. Three keys, each held by a different officer, must be inserted in a control panel. Additionally, authorization from Moscow must be obtained via automated radio link; this procedure requires a disk kept locked in a safe, which is opened with yet a fourth key.^#However, this key is held by the submarine's captain, who also holds one of the three launch keys.

Literature

• The safe deposit vault that Artemis Fowl burgles in The Opal Deception has a lock system like this. Artemis gets around it using an ingenious extending pole disguised as a collapsible scooter (to get it past security).
• Deathlands. In "Ice and Fire", three keys are required to open the molly-guard over a Big Red Button. As the places where the keys were kept are likely nuked out of existence, a tiny charge of C4 does the job instead.
• An escape hatch in Thursday Next: First Among Sequels has two handles which need to be turned simultaneously.In a touching Redemption Equals Death, Evil Thursday chooses to help Thursday escape, knowing that she herself has no way out.
• In the Gears of War novel, Jacinto's Remnant, Chairman Prescott, Colonel Hoffman and somebody else had to insert three keys and turn simultaneously to activate the Hammer of Dawn technology that destroyed most of the planet. Prescott had it next to his car keys.
• In the Mass Effect novel Ascension, Hendel and the one of the quarians had to this to a bomb that is rigged to explode and destroy a ship with a crew of over 500. With the added problem that they couldn't see each other.
• In The Baroque Cycle, the Pyx is locked with three different locks and, later, kept behind two doors which are each locked with three locks. That doesn't stop Saturn from picking them and getting into it.
• The Lord Darcy story "A Case of Identity" had a two key system for a vault containing the Marquis' official regalia. The door had eight keyholes and two keys. Each man with a key knew which keyhole to use his key in, but not which keyhole the other key went into. Improper timing, or turning a key in the wrong hole, would set off the alarm. The keyholes were usually covered with ornamental doors; when opened, they acted as visual shields so that neither man could see which keyhole the other picked.
• In Neuromancer, the artificial intelligence Wintermute can only be freed from its programming constraints if one person speaks a password into a particular computer terminal just as another one breaks through the software defenses.
• From the Coldfire Trilogy, the vault in which the holy relics of the failed Crusade against the Forest are stored behind a two keyed lock. The Patriarch holds one key.
• In The Good Thiefs Guide To Amsterdam, each of three thieves keeps one of the three keys needed to open the safety deposit box that hold the fortune in diamonds that they stole. One of the three thieves hires the protagonist Charlie to steal his partners' keys.
• In The Sum of All Fears, not a physical lock, but when President Fowler orders a nuclear strike on Iran, he has to get it confirmed by someone else from an approved list. Since both the secretaries of State and Defense are dead, he tries to get CIA Deputy Director Jack Ryan to confirm the order. Ryan refuses, since it's an act of Disproportionate Retribution, using a nuke to kill one man. Turns out to be the right call since Iran wasn't actually behind the nuclear attack at the Super Bowl.
• Averted in Big Trouble, where a nuclear bomb in a suitcase gets lost in Miami.
  "Could they set it off?" asked Baker. "I mean, doesn't it have, like, whaddyacallem, fail-safe things?"
  "This thing wasn't built by good guys," Greer said. "It's not like in the movies, where the president has to give the Secret Code and two trusty soldiers have to turn their keys simultaneously. This thing was built by bad guys who wanna be able to set it down in a public place in a crowded city and arm it quickly."
• In Ready Player One, the third gate requires three people to open it at once. This slows down IOI when they get to the gate first, because it appears to only be one keyhole; the trick to having the other two show up is to have three people sing the Schoolhouse Rock! song "Three is a Magic Number".
• Star Wars Legends:
  • In The Truce at Bakura, it is revealed that on Imperial ships the Self-Destruct Mechanism consists of two levers that when pulled together will trigger an immediate reactor overload. While there aren't actual locks, the levers are at opposing sides of the bridge to prevent accidental triggering.
  • Star Wars: Allegiance: Mara Jade's field gear includes a lightsaber hidden inside an innocuous-looking data analysis unit. The unit has three hidden catches which must be tripped simultaneously to open it, only two of which can be reached at once by humanoid beings. Mara uses her hands on those and trips the third telekinetically with the Force.
• Prince Roger: You only need one key (of four entrusted to various senior officers) to activate the self-destruct on a Saint ship, but you need at least two keys to deactivate it.
• Wrath of the Dragon King has a variant with Humbuggle's Game at Stormguard Castle. In order to advance to the next stage of the game, three coins need to be found and thrown into the fountain in the center of the castle simultaneously. However, the coins are enchanted such that any given person can only hold one coin at a time, so at least three separate people must be working together to advance the Game.

Live-Action TV

• Rare example not involving nukes: in an episode of Alias set in a Romanian mental hospital, the door to get out is double-keyed, one lock on the wall to either side of a wide maintenance door, too wide for one person to turn both keys with their hands. Sydney deals with this by acrobatically turning the other one with her foot.
• In the Andromeda pilot episodes, Dylan gives four people he barely knows positions on his ships - because, apparently, one person cannot launch the Nova Bombs even though one can arbitrarily give out the positions necessary to do so.
  • Pops up again in the last season where a pair of (stupid) gang leaders join forces to shake down the locals. They find a key to open a ship they want. Only at the moment when they both have to enter the keys to get the door open they get greedy and turn on each other.
• In Battlestar Galactica (2003), the nuclear launch tubes on battlestars are controlled by two-keyed locks.
• Batwoman (2019). In "Through the Looking-Glass", supervillain Alice has to get the help of her sister Kate to break Mouse out of Arkham Asylum, because he's being held in a maximum security isolation ward that requires two keys to open, one kept by the Head of Security and the other by the doctor treating Mouse. Averted in a later episode when Alice is able to activate the switchboard to open every cell in Arkham using only a single key.
• Doctor Who:
  • "Journey's End": The Osterhagen Key, a Self-Destruct Mechanism for the Earth, can only be activated if three out of five stations are manned.
  • "Dinosaurs on a Spaceship" has a manual override for the navigational system that requires two people "of the same gene-chain" to unlock it and pilot the ship. Fortunately any old DNA will do, and not just the DNA of the builders.
  • Averted in "Cold War": the launch control system of a Soviet nuclear submarine allows an Ice Warrior to retarget its missiles and ready them for launch using a single key taken from the executive officer. It is an aversion, since the plot hinges on this being possible, but ultimately we don't get to see if the two-key security actually was compromised.
  • Averted in "The Day of the Doctor", when Kate Stewart is able to order the destruction-by-nuke of the Black Archive by herself.
• Kamen Rider Geats: In order to grant the wishes made by Desire Grand Prix participants, both the Producer and the Game Master have to approve said wish, using their respective Vision Drivers as authorization. Though as it turns out possessing both Drivers is all that's necessary.
• Madam Secretary. A computer glitch makes it look like Russia has launched its nuclear arsenal at the United States. The ABORT signal is sent just as an ICBM technician has turned his launch key, then a Reveal Shot shows the other technician was a fraction slower and his key hasn't been turned yet.
• Used in NCIS: Los Angeles when the team has to access a dead man's safe-deposit box, thinking that it contains a little black book of highly classified and potentially damaging secrets. Once they've found the dead man's key, they still have to send in Sam Hanna as his attorney.
  • In another episode three launch officers stationed in nuclear missile silos are revealed to be moles for a radical organization. Two of them end up stationed at the same silo but a failsafe prevents them from launching their missile without an authorization from the President. However, the system has an override that can be activated by the two launch officers of another silo. One of those people is also a mole so he kills his partner and then gets around the two key lock by using a mechanical device that turns both keys at the same time.
• During the first season finale of SeaQuest DSV, Captain Bridger and Commander Ford use their keys to arm the ship's nuclear warheads as a Self-Destruct Mechanism to seal a massive crack in the ocean floor.
• Referenced in an episode of Seinfeld, where George's girlfriend refuses to accept their break-up. Both she and Jerry compare this to launching missiles from a submarine (Jerry says it's not the same, but George's girlfriend says it is).
• Smallville: A villain manages to activate a nuclear silo by threatening the operators to help him turn the keys. Then he kills the operators anyway. There's a reason real-life nuclear silo operators are trained to die before giving up their keys.
• Stargate SG-1:
  • The passwords of two officers are required to cancel the Self-Destruct Mechanism. Though it varies: in "Menace", Hammond and Carter turn it on and off with keys. In "Lockdown", O'Neill and Kearney turn it on with keys. In "Lockdown" and "Avatar", Carter turns it off in the control room by tapping the computer a bit.
  • Once on Stargate, a possessed O'Neill tells another guy at gunpoint to insert his key, which is defeating the purpose — you'd think they'd tell the people with keys to die rather than be coerced.
  • Putting this trope into effect in Stargate SG-1 could almost have been considered a plot thread of its own during the first two seasons or so. In the movie and until the events of the pilot, the SGC had a hair-trigger on the self-destruct button and the Gate's iris, because the primary priority was keeping everything alien out. In the show, though, they start bringing stuff back for study and all kinds of other reasons, and of course, it's stuff they don't fully understand that's often hostile. A Two-Keyed Lock is needed to stop Puppeteer Parasite, a handprint scanner is needed to stop cloaked aliens, and so on.
• Star Trek:
  • One can actually see this decay in the franchise. In the days of the original series, voice-print match and codes from three senior officers are necessary to activate the auto-destruct sequence. In the days of TNG and DS9, it only takes two with biometric hand scans, and requires both to disable it. By the time of Voyager, Janeway could apparently destroy the entire ship on a whim.
  • Played with in the episode "Cathexis". An alien consciousness is floating around Voyager, possessing various people long enough for them to enter various commands in their computer, then moving on. At one point Janeway considers dividing the command codes between herself and the security chief, as the alien can only possess one person at a time.
  • This actually becomes a plot point in "11001001". The Bynars load the Enterprise's main computer with all the data from their home planet. In order to download it back into the planet's mainframe, a passcode needs to be entered. However, since the Bynars always operate in pairs the passcode has to be entered at two separate terminals simultaneously.
  • The Xindi planet killer required access codes from any three of the five members of the Council in order to fire. This would've been a useful feature when three of Council races back out. Unfortunately, the Reptilians and Insectoids abduct Hoshi and force her to crack a third code. By the time the Insectoids realize they've been played, they've already supplied their code and as such aren't needed anymore. Interestingly, while arming the ship requires three codes, launching it can apparently be done with two.
  • In the TNG episode "Interface", it's explained that it requires two senior officers' authorizations to deactivate the holodeck's safety protocols (though some subsequent TNG-era stories ignored this detail, e.g. Star Trek: First Contact has Picard disengaging the protocols by himself).
• Stranger Things: Season 3 has the Key, the machine that the Soviets are using to open a portal to the Upside Down, and which can only be turned on or off by a two key system. In the season finale, with Hopper too busy fighting Grigori to turn one of the keys, Joyce wraps her belt around one, giving her just enough room to reach over and turn the other by hand while the belt turns the first.
• Supergirl (2015): Indigo manages to infiltrate a nuclear silo, but is informed that she can't turn the keys on her own. She just kills everyone else and stretches far enough to turn the keys herself. While it doesn't get much attention in this episode, it's part of the running theme that Earth has a lot of trouble anticipating alien abilities.
• In the second V (1983) miniseries, the Visitors intend to deploy their mothership as a nuclear bomb as a last resort in case their troops can't hold on to Earth. John and Diana both take one of the arming device's two keys. John is willing to concede defeat and just retreat, but a spiteful Diana wants to kill off all of humanity because they defeated her. She orders John to hand over his key at gunpoint, and kills him when he voices his disgust.
• In Krypton, The seal on Doomsday's vault requires blood samples from two distinct sources: the House of El and the House of Zod, who originally sealed the monster away. A time traveling General Zod eventually realizes that as the son of Seg-El and Lyta-Zod, he has the blood of both families and can open the vault on his own.

Roleplay

• The second site Hua Yin explores in The Dao of the Awakened has a door requiring simultaneous channeling of Qi at two points too far apart for one person. Later, there is a bridge which must be maintained active by one person while another crosses.

Video Games

• Chase the Express have you obtaining a locket from Ambassador Pierre's daughter, Jane, after rescuing her from terrorists, where she gives you her locket as a "Good Luck Charm" as you try rescuing her father. Turns out said locket hides one of two keys to unlock a vault containing blueprints for a high-tech hydrogen engine, and Ambassador Pierre holds the other; you both unlock said vault in a subsequent cutscene.
• Chip's Challenge: A unique version appears in the 121st level, Perfect Match. There's a meandering corridor from whence cloned fireballs are moving to die in a moat of water. Right in front of the clone machine is a toggle door that opens and closes when the level's green buttons are being pressed. Ideally, the door should be closed so the corridor clears up and Chip can reach the exit, but in the central area of the level there are two paths where fireballs move, and each path happens to have a green button as well (and they're pressed whenever Chip or a mook steps onto them). The trope comes into play when Chip makes it so those two buttons are pressed at the same time, canceling out the toggle command and leaving the clone machine's door in its current state (open or closed); this is easier said than done, because it requires pushing a block to kill any surplus fireballs in one of the routes (the other cannot be manipulated), and any mistake will require him to clone new fireballs in that route to recalibrate. Chip can then press a green button in his area in case the toggle door remains open (after the fireballs' pressing match is done) in order to close it, allowing him to finally reach the exit.
• Devil May Cry 4: A gate in Mission 11 requires the pressure plates on both sides to be stepped on so that it will open. Nero can just easily snatch the nearby Scarecrow on the other side to get past this. In the Special Edition, the gate is already open when playing as Lady or Vergil because they lack the necessary ability to pull in other enemies.
• Metroid Prime 3: Corruption has you do this with a GF trooper in order to activate an elevator. The "trooper" in question is the shape-shifting foe Gandrayda.
• Resident Evil:
  • Oddly enough, only two "puzzles" in Resident Evil 4 need Leon and Ashley to do this.
  • However Resident Evil 5 has loads of these to prevent you from leaving your partner behind.
  • Resident Evil 0, considering its focus on the partner system, also had a few puzzles like this, including one literal two-keyed lock right at the end.
  • Resident Evil 6 has random doors all over the place that require two people to hold down buttons on either side of the frame for them to open. Nothing valuable is behind them, they're just another way to make sure you don't leave your partner behind.
  • Resident Evil – Code: Veronica has one such lock to the weapon used to defeat the Final Boss. Chris and Claire activate it in a cutscene before the final battle.
• Final Fantasy:
  • Used as a minigame in Final Fantasy VII, where to open a security door three party members must push three widely separated buttons at the same time, the player only controls Cloud and has to timed their button press with Tifa and Barret's automatic button presses.
  • The Four Shrines in Final Fantasy IX must be activated simultaneously, but the only impact this has on gameplay is forcing you to fight a boss with just two characters; you don't control the rest.
  • Similarly the Fork Tower in Final Fantasy V. The tower will explode if both rewards aren't taken simultaneously, so you're forced to split the party. This isn't an idle threat, either - once one party takes their item, the game switches to the other party, and if you don't grab the item within about a minute you get a Nonstandard Game Over.
  • Final Fantasy XI has the Three Mage Gate, which requires three different classes of mage to stand on panels to open initially, though once you pass the gate, you can obtain a charm that allows you to open the gate yourself.
• Done in Modern Warfare 3 in a mission where you play as Frost and have to infiltrate a Russian submarine. The level has you launching missiles from the sub onto the other Russian boats, but before you can do so Frost and Sandman have to use a two-keyed lock to open the button that launches the missiles. Sandman also apparently gets both keys from the Captain, which does seem to defeat the point; but then again, they aren't nuclear missiles.
• Happens all the time in Gears of War 2.
• In Metal Gear Solid, the player must find three card keys to deactivate Metal Gear Rex late in the game. The twist, however, is that the one key Snake obtains is actually all three keys. The key is made of shape memory alloy, so depending on what extreme temperatures Snake subjects the key to, it changes into each of the keys.
  • There's also a two-part code, each part memorized by DARPA chief Donald Anderson and ArmsTech president Kenneth Baker, respectively. The PAL key option is stated to be a backup, as a way to disable Rex once the code has been entered, or to enable it if the code is somehow lost. Snake is led to believe Psycho Mantis extracted Anderson's code, even though it should have been impossible, while Baker gave in to Revolver Ocelot's torture. It turns out Ocelot inadvertently killed Anderson before getting him to break, requiring Decoy Octopus to impersonate him and have Snake figure out the key system so they could activate Rex.
• Sonic The Hedgehog:
  • Used in Sonic Chronicles: The Dark Brotherhood when you had puzzles where four characters had to stand in certain spots to unlock doors.
  • This is also a common type of puzzle in Sonic Heroes, where all three teammates have to stand on switches at the same time to activate a door or gimmick. While at the start these puzzles boil down to running through a line of switches in Power formation, later stages have the switches located in completely different corners of an area, resulting in a hybrid Escort Mission and No-Gear Level where you have to leave your teammates behind at switches as you travel to the next while making sure said teammates remain safe.
• Half-Life:
  • The two scientists who let you into the Anti-Mass Spectrometer chamber have to operate a pair of retinal scanners simultaneously to open the door.
  • Unfortunately frequent in the PS2-exclusive expansion Decay, where the designers' idea of co-operative gameplay was to include puzzles that require two players to work synchronously to be solved efficiently, such as turning switches on opposing sides of a room simultaneously.
• A few 'double-button security locks' show up in Sly 3: Honor Among Thieves. The timing window seems to give some margin of error. Notably, while there are many Two Keyed (and more commonly three, five, seven, or whatever-keyed) locks, these are clustered on the console as individual padlocks. Still, you do have to retrieve all the keys to open it.
• Done, sort of, in Fur Fighters in a submarine. The player must turn two keys at the same time but instead of getting two people you just back into one key and shoot the other to make them turn.
• In Jedi Knight II: Jedi Outcast, the prison where Jan is kept is like this, with about five or six consecutive doors. Holding down the switch in between two doors holds those two doors open only, so you have to open the doors, wait for Jan to walk through to open the doors for you, and continue until you leapfrog your way out.
• Happens all the time in LEGO adaptation games. Many doors can't be passed unless two (or more) characters simultaneously throw switches. Thankfully, unlike many games, the AI is smart enough to move some distance to the other switch, without having to carefully babysit them through each step.
• Opening the shuttle bay door in Space Quest 6 requires two people (or one person with another person's arm appendage). Interestingly enough, this trope is inverted any and all of the auto-destruct sequences in the series.
• One update of a Let's Play of the Dwarf Fortress map BoatMurdered had someone submit a drawing of the employment of the "lava death system." With two keys, natch. In the actual game, of course, the system was activated by a simple lever.
• One bank that Sam Fisher has to infiltrate in Splinter Cell: Chaos Theory has a two keyed lock protecting its main vault. Fisher, however, has a remote-controlled key-turning device.
• The Legend of Zelda:
  • The Legend of Zelda: Majora's Mask has plenty of these in the Stone Tower, and in order to work them you need the Elegy of Emptiness, which creates a statue duplicate of your form, and the Zora and Goron masks (Deku Link's statue is too light to be used for switch pressing).
  • The Legend of Zelda: Four Swords: There are a lot of puzzles which include the "four buttons, each of them only triggers if a person is standing on it"-factor. In some of the games this is subverted by "one player controls four characters". At some places this is required to move on, at others it's just "drop a lot of loot"!
  • The Legend of Zelda: Spirit Tracks: There's a good number of two-keyed puzzles in the game. Sometimes using a block or the assistance of lovely Princess Zelda (as a Phantom) to push one, or hitting a series of switches with the boomerang.
• Oddworld - Abe's Exoddus has a lot of these. Abe can turn one wheel, but there's often more than one required to unlock a door/move a platform/whatever, so you need to bring other Mudokons along and order them to turn the wheels. The timing's fairly forgiving, so assembling the Mudokons is usually the main problem... with one exception, where it's two levers instead of wheels.
• One way Banjo-Tooie enforces use of the Split Up mechanic is by having doors that open only when two Pressure Plates are occupied by a bear and bird at the same time.
• Mario Party:
  • Mario Party 5: In the minigame ID UFO, two pairs of characters have to press the UFO icons that match the ones shown in front of them. The caveat is that, for each team, the two correct icons have to be pressed at the same time (each by one character), and doing so grants a point to that team while replacing all present UFOs with the next batch. Whichever team manages to score three points will win; but if neither succeeds at that after 60 seconds, the minigame ends in a tie.
  • Mario Party DS: In the minigame Cube Crushers, two teams of characters are navigating through a maze filled with breakable ice cubes, and at the end of each room there are two switches that open the door that leads to the next part. Each team has to punch the ice cubes to break them (they must be careful not to break certain cubes marked with a question mark, as they may end up freezing for a short time; other blocks have a Starman that helps them break stronger blocks, though) and reach the switches, which have to be punched at the same time (each switch is located in a side of the door, so it's required that the two characters approach them separately) so the door to the next room opens. A total of three rooms awaits for each team, and in all cases the door has to be opened the same way. The first team to reach the exit wins.
• Skies of Arcadia has a whole dungeon focused around locks that require two people to stand on panels in different parts of the dungeon. The thing is, neither side knew that they were helping each other get past and they just both happened to be searching for the same treasure at the same time(for a double dose of irony, it was to make enough money to go looking for each other).
• Ratchet & Clank Future: A Crack in Time includes a variation of this. Clank must use his newly-acquired ability to shift time to record multiple copies of himself completing various tasks (such as pressing buttons or activating platforms), usually with the end goal of opening a door at the end of a room. The actions of the copies must be perfectly timed in order for the player controlling the "real" Clank to solve the puzzle; with up to four copies working at once to complete the task, the difficulty can ramp up pretty quickly.
• Mortal Kombat: Shaolin Monks has a bunch of these. They're completely optional secrets/goodies, and in no way necessary to continue the game. They ARE, however, essential to 100% completion. If you're a completionist, and you don't have a sibling or buddy to play the game with, don't get the game.
• Portal:
  • The games use a few of these in both single-player and co-op. The former involve two buttons that need to be pressed within a short timespan of each other, and thus require having your two portal ends right next to them. (One of these is justified as an actual two-keyed security lock. The rest are just part of the tests.) The latter actually involve both players, and the game has thoughtfully included the ability to initiate a countdown that appears on the other's screen.
  • Subverted in Portal 2, where a timed two-switch interlock to open a blast door is defeated by using the portal gun to cross the entire fifty-foot wide room to hit both switches within the time limit, rendering the safety spacing irrelevant.
• Ōkamiden being based around partners has a plenty of these throughout the game where Chibi and his partner must stand on pressure pads to unlock doors or make bridges appear. One notable example has a two-buttoned lock which is also a trap forcing Chibi to play through half the dungeon himself to gain the key to free his friend.
• City of Heroes (as well as some other MMORPGs) have missions where a given number of people must trigger some kind of switch simultaneously (or within a margin of error given lag times) in order to complete.
• The Elder Scrolls V: Skyrim: The vault of the Thieves' Guild has one of these, with the keys being owned by the most powerful members of the guild. No one realizes it's already been emptied by Guildmaster Mercer Frey, using a magical lockpick he stole from the goddess Nocturnal.
• In the "purple world" of Braid a few parts require synchronized or simultaneous flipping of switches or unlocking of doors, using that world's gimmick.
• RuneScape:
  • The Dungeoneering skill has two variants on this, in the lever room and follow-the-statue-leaders emote rooms.
  • Getting to the king dagganoths requires two people (or one person and a pet rock) to get past any of the three entrances to the monsters, then three people (each having gone down a different path) to open the door to the kings' lair. The rune thrownaxe was later introduced to circumvent it, as its special attack lets it ricochet off of all three ends.
• Present early on in Deep Fear, as you have to get the two keys from the people charged with their safekeeping (both incapacitated) to abort a nuclear missile launch from a damaged submarine. Although, both slots are within arm's reach from a single spot...
• Fatal Frame II / Project Zero 2 has a couple of places where the twins have to stand on pressure pads to unlock certain doors. Seeing as the village had been completely cut off from modern technology it's rather out of place to the general rural-rustic style.
• Darksiders II has few. Several dungeons has Death commanding up to ghosts which results in many cases of this. Then later in the game Death gains the ability to split his soul into two which generally follows this trope more clearly as you have to control both to perform the same actions at the same time.
  • It also turns out the that the final door in the game requires two keys, and they have to be turned at the same time for the door to open.
• The Cave has several puzzles require characters to pull switches/stand on pressure pads to allow other characters to past. Also a literal three-keyed-lock is in the scientist level. This is in fact a central theme of the plot: the parties exploring The Cave are complete strangers with nothing in common save that they all have goals they can't seem to achieve, and this place makes those goals achievable - but not without the assistance of said strangers. This trope is thus pervasively used (both out-of-game by the designers and in-game by The Cave itself) to turn What You Are in the Dark into a group experience.
• A small example in Mega Man X: Command Mission: the intro stage involves waiting for a certain tone from Zero to hit a button and unlock a set of doors. Subverted in that Zero is controlled by the game and not the player. And your reward for messing up the timing? A battle against three Preons.
• A very common puzzle type in Deadly Rooms of Death. As you only control one character, such puzzles generally require manipulating monsters so they move onto pressure plates at the correct time.
• Both castles of Dhaos in Tales of Phantasia feature doors that can only be opened when 4 (and later 5) people stand in front of them, basically ensuring that the player has to reunite the party.
• In Spider-Man: Shattered Dimensions, the 2099-verse frequently requires two or more scientists working at separate consoles to open a door. Your job is to keep them alive until they've done it.
• Syndicate (2012): The door to the Eurocorp Data Core is protected by one of these, theoretically making it the most secure room in the entire facility. However, because both key terminals are not immune to hacking and the timespan needed to activate both locks is rather generous, a single Agent with a DART 6 chip can hack both locks rapidly in succession, completely bypassing the security system.
• One quest in The Elder Scrolls IV: Oblivion involved a trio of treasure hunters protecting their loot with, among other things, a chest with three locks, with one key per hunter. Predictably, one of them gets greedy and murders the other two for their keys. After hunting him down and killing him, you get all three keys from his corpse and, thus, their loot as your reward.
• In Infernal, Lennox can use his demonic teleportation power to deal with these, moving from one to the other quickly enough for it to work.
• In Dragon Age: Origins, there are two such locks that the Mage Warden must overcome. The first requires a password passed down through the Chantry followed by a spell by a mage that has passed the Harrowing, the second literally requires two keys, one held by First Enchanter Irving, and the other by Knight Commander Gregor. The keys are needed because the second door has Anti-Magic properties preventing the Warden from just blasting through it.
• In Ys: Ancient Ys Vanished ~ Omen, the second boss requires two keys to access, unlike the others. Though in this case it's two sets of locked doors that one man can open sequentially, as opposed to one door that has to be opened by two people simultaneously.
• PAYDAY 2 has a couple of examples. Two vaults in the game require two key cards to open. Shadow Raid's vault holds the very valuable Samurai Armour, whereas the vault in GO Bank contains all of the deposit boxes that the players need to open to finish the heist.
• Tales of Xillia has a gate that needs to be opened by two switches being charged with mana at the same time. The player is led to believe it'll be a timing puzzle like in Final Fantasy VII, but the whole thing is done automatically via cutscene. The point of it is just to show that Leia isn't very good at channeling mana.
• Used occasionally in Star Wars: The Old Republic, particularly for obtaining a few of the datacrons hidden throughout the game world. This can be rather frustrating, as it's sometimes difficult to find another player willing to perform the task with you.
• In some missions in Warframe, you may encounter doors that require two players standing by their control panels in order to open. If there is only one player in the squad, activating one of the panels will suffice.
• Astral Chain has a few puzzles in which you must stand on one switch and your Legion must stand on the other at the same time to unlock a door.
• In Dreamfall Chapters, the gates in the tunnels below Propast require two people to push buttons simultaneously to open them.
• The door leading to Dr. Kirk's personal lab in Dino Crisis is locked by two key cards. When Regina has both cards in her possession, she calls Gail over so that they can swipe the cards on both key card readers at the same time to unlock the door.
• Used for drama in Iconoclasts with the rocket launch to the small moon. One of the two parties doesn't want to activate the rocket because it means the likely death of Robin, the main character, in spite of her deeming the risk worth it and wanting to go.
• Anarchy Online has Crypt of Home, which has doors that take it a step further. To progress, two people must activate switches on opposite sides, let a third person in, and have the third person keep the door open via another switch so everyone can pass.
• Tormented Souls: The door to the bunker is locked by two widely separated retinal scanners. The cult is keen on twins, and the idea is that the door will be only unlocked by having one identical twin at each scanner. Caroline needs to get in, but there's only one of her. The solution is to go back in time to the beginning of the game and remove an eye from Caroline's unconscious past self to place next to the other scanner, thus solving the mystery of why Caroline woke up at the beginning with a missing eye.
• Robot Odyssey has a progressive series of these, starting with having to coordinate two robots to complete a task, to the culmination of the fourth level requiring all four robots to separate operate their switches to free a fifth robot. Then, in the fifth level, those five robots need to work together in programmed coordination to solve the final puzzles.
• Transistor: In the tutorial area, Red has to use Turn() to speed herself up enough to activate two Break Points at nearly the same time to unlock the path forward. Without Turn(), each Break Point relocks too fast for both to be unlocked at the same time.

Visual Novels

• Snatcher has a three-keyed one in located in Queens Hospital.
• Hotel Dusk: Room 215 has you fix the lights to a room, which requires that you turn on both switches required to allow the lights to turn on at the same time. This would be fine if it weren't that the touch screen works against you.

Web Animation

• In Brain Divided, when Jon's right and left brains finally settle their difference, they both turn a key to prompt Jon to confess his love to Scarlet.
• At the end of an animated music video for Rasputin by Boney M, the three scientists are shown engaging a three-keyed lock when the situation becomes hopelessly dangerous.

Webcomics

• Used here in Goblins, with a four-key system. A giant just smashes the door open for them, because they REALLY don't have time for puzzles.
• In The Mansion of E, Carmal uses the existence of such a system to deduce that a certain machine is more important than she had been aware.
  Carmal: The only sane reason for the... thingamabob builders to make it that way would be... they didn't want people just casually turning it on, or changing it, or whatever the zark we're doing.
  Shabash: Figured that out all by yourself, did ya? Yeah. The thingamabob is important.
• xkcd uses a two-keyed missile launch system to make an analogy about cyclical software security development. A device is developed to make the launch system more convenient to use by allowing one person to turn both keys—but since that's a security risk, the device itself is then locked with two keys.
• In Axe Cop when they're visiting Magic World they have to insert two magic wands on the side of a gate at the same time to get in. Not that they get very far after that point.
• Starward Lovers: The door to the core module requires two agents to open; two switches set a distance apart must be pulled simultaneously.

Web Original

• Atop the Fourth Wall uses the exact self-destruct code from Star Trek III in the Cold Open for his review of... the comic adaptation of Star Trek III in order to prevent Lord Vyce from taking his ship back. Vyce manages to stop the sequence before the ship blows up. Possibly unique in that one of the people who confirms the code is the ship's AI. Linkara makes it clear that he's not asking her to help kill herself, though, as she can transfer her consciousness off the ship.
• In Freeman's Mind, Gordon accidentally launches what he believes to be a missile (it's actually a satellite delivery rocket, but he hadn't been paying attention to the security guard who told him about it) and afterward mentions that he would have expected one of these instead of just the Big Red Button he pressed. Even for a satellite delivery rocket, and even considering he was resuming an aborted launch, yeah, you'd think the procedure would be at least a little more complex.
• Joked about in a What If? entry with the National Weather Service having a special snow measuring board:
  Scientist 1: It's snowing. We'd better go get the board.
  Scientist 2: OK. You'll need to come along since we need two people to turn the keys to access it.

Western Animation

• The Fire Temple's inner sanctum in Avatar: The Last Airbender can only be opened by five simultaneous fireblasts. A "fully realized Avatar" could do it single-handedly, but it otherwise requires five powerful and fully-trained firebenders.
• In Chaotic, the Doors of the Deepmines, that act as the M'arillians' prison requires four keys held by the other four tribes to open.
• One of many many secure location tropes parodied in a Family Guy "found a new place to hide my porn" sequence.
• In Gargoyles, when Halcyon Renard's second, fully-automated airship is sabotaged, he goes to the bridge to take it off a collision course, only to realize that two people are needed at two different consoles to perform emergency course corrections.
• The Simpsons:
  • In "Hello Gutter, Hello Fadder", two keys were required to be turned simultaneously to drop the "perfect 300 game" balloon at the bowling alley.
  • In "HOMЯ", When Homer goes to the bank to withdraw his family's life savings, he's informed that the money cannot be withdrawn unless both he and Marge agree to it. He goes to the other side of a nearby plant to pretend he's talking Marge into agreeing and then he forges her signature. He also pretends Lisa is there asking for a bonbon.
  • In Season 29's "Gone Boy", Bart stumbles into an abandoned missile silo, and after the Springfield police call off the search, Sideshow Bob hears a news bulletin that Bart is reported to be dead, only for Marge to confirm that he's still alive. After Milhouse leaves the Simpson house, Bob asks Milhouse to lead Bob to Bart's whereabouts in the missile silo. Bob ties Bart and Milhouse to the missile, which requires a two-key setup to ignite, and after stretching his body, he manages to ignite the missile, only to untie Bart and Milhouse from the missile, which lands near the sculptures in the town plaza.
• An episode of the animated Dilbert parodies this: while Dilbert and Dogbert are stuck behind a driver at a tollbooth, they engage a dual-keyed weapon to destroy her vehicle.
• The story arc of My Little Pony: Friendship Is Magic's fourth season involves a six-locked chest that appears after the Elements are returned to the Tree of Harmony in the second half of the season premiere. Each of the Mane Six's keys is a memento given by a supporting character when they both learn a lesson about friendship.
• Ben 10:
  • Ben and Kevin hacked the Omnitrix offscreen in Ben 10: Ultimate Alien to ensure he wouldn't turn into Alien X by accident- a Reality Warper with the huge drawback of a conflicted mind that can't seem to agree on any mode of action- without using two keys to access it on the transformation options screen in case the Godzilla Threshold was crossed.
  • Earlier on in the original series, the energy source hidden in the Plumbers' base at Mount Rushmore can only be accessed with two special keys hidden on opposite sides of the country.
• Gravity Falls: In "Not What He Seems", Dipper, Mabel and Soos turn three keys together to reveal the emergency shutdown button for the interdimensional portal.
• Codename: Kids Next Door: One episode features a room where the way in cannot be unlocked without two high-ranked operatives inserting their boogers and reciting their respective passcodes.
• Batman: The Animated Series: In "The Lion and the Unicorn", the missile requires two codes. Alfred knows one and Freddie knows the other.
• Avengers Assemble: One episode of the Black Panther's Quest arc features a door that cannot be opened unless an Inhuman and a member of Wakanda's Royal Family open it together.
• Spoofed in Harley Quinn (2019). In "So You Need A Crew?", Harley is trying to steal a nuclear weapon behind a door. She finds a key and goes to open the lock, only a second lock activates. She finds the second key and with some trouble is able to turn both keys by holding one in her hands and the other in her toes, only for a third lock to activate above the door. Then the Joker walks in with three goons who get the door open easily.
• In the animated short Dinosaurs: The true story by Paul-Louis Aeberhardt, the dinosaurs prepare to launch their nuclear arsenal to destroy the incoming meteor. The nukes are activated with a three-panel handprint scanner. The Pteranodon scientist activates his, the Ankylosaurus general activates his, then the President...is a T. rex whose tiny arms can't reach the scanner.
• Sonic Boom: "The Curse of Buddy Buddy Temple" features, unsurprisingly, a temple with the theme building team-ship, which doesn't sit well with the two trapped people, Sonic and Dr. Eggman. Inside they have to alternate switches from across rooms to get across lava pools and the classic needing to press buttons at the same time to open doors.

Real Life

• Truth in Television, this, especially in terms of US ICBM silos. The two key slots are far enough apart that one person can't turn both at the same time. Plus you'll need the launch codes, if they're not set to 00000000...
  • Yes, that actually did happen.
    • Permissive Action Link. Under the Kennedy administration, somebody decided to put PALs on the US nuclear arsenal to prevent unauthorized firing. SAC objected to this practice, fearing the possibility that the launch codes would not be available in time of need. So, very quietly, SAC installed these devices, intended to ensure the safety of the free world, and very quietly, they set the combination on every single one of them to 00000000. Very trusting people, SAC.
    • Well, their trust appears to have been well placed.
    • The logic was that warheads mounted to missiles in either ground-based stations or in ballistic submarines are secure because of the two-man-rule interlocks, and PALs would risk a loss of readiness without significant security benefit. Actual (non-trivially-coded) PALs were (eventually) applied to small warheads - air-dropped bombs and ship/air-launched cruise missiles. These warheads, unlike those for ballistic missiles, can be stored or transported in a functional or semi-functional state and thus may be lost or stolen. For these weapons, the two-man rule utilizes the PALs themselves - two officers must concur with the legitimacy of a nuclear launch order and release their portions of the PAL codes, or else the warheads cannot be armed.
    • The all 0's code was also applied to the missiles themselves, but not the warheads. Also, there would be more than one control center for any squadron of missiles, and a complete launch would require the cooperation of all of them, not just two people.
    • Aside from PALs, strategic warheads (like those used on ICBMs and SLBMs) have to meet a myriad number of environmental conditions (like flight time, acceleration, aerodynamic forces) throughout its travel to enable detonation. This essentially makes the Earth a "third man" in the process.
  • The entire launch process required two men before even getting to the point in which they turned the keys. A nuclear launch would begin with the transmission of a 35-character code message, such as "Golf-Hotel-6-2-7-Alpha-etc." The commander and his deputy would then write the code in a notebook and compare what they had written once the message had concluded. Having agreed that they had both written the message correctly, they thus had a "valid message" and could open the locked red safe. Both officers had their own combination for a lock on the safe, so they needed to agree to open it. The commander would check the first two characters and find an authenticator envelope with those two. If the plastic "cookie card" inside the envelope matched the last five characters of the message, then it was not a drill and they had permission to insert their launch keys. Hidden inside the message was the ordered launch time and also the unlock code for the missile, which then opened one of the four fuel/oxidizer inlet valves, kept locked to prevent an unintentional or unauthorized launch, and begin loading the missile with the fuel needed to reach its target. Once the keys were turned and the "launch enable" light came on, the missile was entirely independent and would accept no further orders from the crew. There was no reset button anywhere. Over the course of just 58 seconds, the missile would charge its batteries, run diagnostic checks by the onboard guidance computer, get loaded with fuel and oxidizer, build up thrust, pop the hold-down bolts, and be on its way, reaching its target only 30 to 35 minutes later.
  • Strategic Air Command also had the "No Lone Zone" rule, or "Two Man Rule," where certain locations in nuclear weapon installations required at least two people to be together, always within sight of one another. This was an airtight rule which could not be broken under any circumstances. One instance of this would be in 1968. Two missile maintenance technicians were servicing a Titan missile, when one fell off the platform to his death below. Since the remaining technician was now by himself on the platform, his superiors had to first report a Two Man Rule violation, then report about the fallen crewmember.
  • One 1980s documentary about a nuclear silo suggested that one man could have launched a nuclear missile by turning the key in his console to activate one "launch vote", and then uninstalling the console, replacing it with another and turning that console's key within a given time, thereby activating the second vote. Although cumbersome, this procedure would not have been impossible.
  • In another version of the Two Man Rule, nuclear missiles stationed in foreign countries had an American officer and an officer of the host nation in possession of a launch key. However it was pointed out that some of those nations (such as Turkey and Italy) had experienced military coups, so the locals could simply hit the American officer over the head and steal his key.
• The Soviets had two launch keys and unlock codes held by the higher-ups (i.e. on shore) for their submarines. Now the case for US subs, but not always.
• For safety deposit boxes, one key is the bank's and one is the customer's. This ensures that the bank cannot open your box without you, and that you (or someone with your key) can't open your box without showing ID to the bank.
  • At least, this used to be the case. Banks are adding increasingly more checks to get in. In the case of one large bank, you must enter a PIN, pass a biometric scan, and use a regular old key as well, constituting three-factor authentication.
• Vault doors also have this in some cases as an alternative to time locks, with two sets of combinations and two dials. It has the advantage of allowing the bank to access the inside of the vault, which in one notable case was useful as thieves had tunneled inside the vault (a slight flaw in time locks as there is no way to look inside the vault if someone is thought to be inside, there is absolutely nothing that can be done).
• Some Soviet nuclear missile silos had three blast doors, each needing three keys, and each key given to a different person. So a total of nine people were needed to actually get access to the missiles.
• In a much more mundane context, most of the rides at the local amusement park won't launch without both operators holding the go buttons, and they can still be locked out by ride sensors. For obvious safety reasons, the ride can be stopped by just one person.
• Many industrial machines have two start buttons, but they are close enough to be pressed by a single operator so long as he uses both hands. The goal here is to ensure that both of the operator's hands are on the control box, and not in the machine. Depending on the machine, there might also be a footpedal.
  • Some machines feature increasing sophisticated sensors to prevent the operator from bypassing the two hand start, which may include interrupted beam optical sensors (defeated by broomstick handles), capacitive finger buttons (hotdogs), and anti-tiedown logic (usually not worth defeating, but sometimes jumped out inside the panel).
• In some poor villages of Africa where they have opted for Food Bank (filled with food aid for use when the harvest is lean and topped up by local farmers when the harvest is good) three people from the community are given keys and required to open it. Because as Josette Sheeran says; food is gold.
• Many main electrical power switches can be padlocked in the OFF position. Devices are available which allow multiple padlocks to be connected to the switch; unless they're all unlocked, the switch cannot be closed. Useful if there might be several people working on the circuit and you want to be sure that it can't be closed unless they all agree. On these, the locks don't need to be removed simultaneously, they just all have to be off at the moment the switch is closed.
• The industrial practice of Lockout-Tagout often includes multi-padlock devices like the one mentioned above. When a major piece of machinery is going to be serviced, you often want to put multiple locks on it so it doesn't start running again unless everyone with a key agrees it is time. The lock will often have a tag attached to it, so you know who to talk to to find out why it is locked-out.
• The Internet Corporation for Assigned Names and Numbers (ICANN) which runs the DNS (Domain Name System) and infrastructure that the entire internet runs on does something similar, though they use seven keys - seven encrypted password keys entrusted to seven different people, which periodically need to be verified with another seven people at a "Root Key Ceremony". The entire event is under extreme security, like out of a spy movie, with hand scanners, secure rooms which no electronic transmissions can escape from, etc.
• German libraries have a long tradition of keeping locked rooms known as the "giftschrank" (literally "poison cabinet") which contained censored writings considered to be hazardous (heretical writings in the past, Nazi literature more recently). In some libraries, the doors have dual locks with keys held by two separate staff members to ensure that only authorized people can access the works.
• Multi-factor authentication is a variation on this idea, where one person is expected to hold all of the keys. The keys themselves are several different types that cannot all be stolen the same way (something you know, such as a password or a PIN; something you have, such as a mobile phone or an ID card; and/or something you "are", such as a fingerprint or retinal scan) to greatly decrease the possibility of an impostor gaining access.
• Among bank accounts with two holders, there are some set so no money can be withdrawn from them unless both holders agree.
• Some online apps, websites, and video games can be set with a two-factor authentication barrier where the user needs both their password and the authenticator's password that's usually generated from a physical device or program. Having both a password and a two-factor password greatly reduces the risk of someone breaking into your accounts since even if they get either your password or two-factor password system, they can't gain access if they don't have both on hand.
• The "Consent Condom", a condom which requires four hands to open, as a statement about the importance of sexual consent.
• Near the end of the Soviet Union, there were two key locks placed on the doors to storage rooms to prevent theft. However this just resulted in either someone just needing to steal one more key than usual, or both people agreeing to steal.

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