Dead-Man Switch

A backup plan in case of untimely death or incapacitation, used as a threat to protect the holder. If that person dies or fails to issue some form of communication within a set period of time, the plan goes into action automatically, making it in the interests of the threatening party to not harm that person. Provided, of course, that the threatening party knows about it. A common plot involving this trope is the switch is put in danger of being set off either by accident or by somebody who had no way to know about it.

A more common twist that is begginning to appear is that of the hero simply cutting off the hand or arm, thereby removing the threat entirely.

If an entire government or culture has a Dead Man Switch, it usually sets off a Doomsday Device.

Named after the Real Life device that stops a train or other piece of heavy equipment if the operator dies, falls asleep, or otherwise loses control of the machine. Oddly enough, though, you don't see it really used on trains in fiction... or cars for that matter. The real life counterpart to the threat aspect of this trope is a fail deadly system.

Load-Bearing Boss is a sub-trope that usually applies to video games.

Anime

 * In Death Note, Rem lets Light know that if Misa dies unnaturally, she'll assume Light did it and kill him.
 * The same series has a variant:
 * There's also the fact that L was able to safely reveal his identity to Light in private, once L made it clear that if he were to die soon after, other people would be able to use it as evidence that Light (the prime suspect) was the murderer.
 * In Eureka Seven, pulls a literal Dead Man Switch upon his suicide, in which
 * In Code Geass, during at the end of season one, Lelouch/Zero straps a bomb to himself that he claims will detonate if his heart stops. The writers admitted that it was added when they realized that otherwise, his opponent would have just shot him.
 * When the cliffhanger is picked up next season,
 * In Hunter X Hunter
 * Itachi Uchiha of Naruto had a few of these. As did.
 * In Detective Conan, Conan employs a Dead Man Switch on a tape recorder
 * Uryuu Minene uses one of these in Mirai Nikki when she holds up a school, derailing an attempt to snipe her because it's attached to a bomb.
 * The Gundam Wing sequel novel Frozen Teardrop has a particularly extreme version of this:

Comic Books

 * The first issue of G.I. Joe Special Missions features a terrorist group who've hijacked an airplane; one terrorist wears an explosive vest with a Dead-Man Switch set to go off if he releases the trigger.

Film

 * In The Usual Suspects, Kobayashi lets the protagonists know that if he dies under suspicious circumstances, his boss Keyser Söze will immediately know who did it and take revenge on them and their families.
 * In Goldfinger, a captured James Bond implies that his death will just activate another agent. It's uncertain if he was bluffing.
 * Or he just meant if he vanished, MI 6 would send someone to complete the mission he failed (and find presumably find out what happened to him)
 * Doctor Strangelove and the whole Soviet "Dead Hand" thing. The big irony in this movie was that the Soviets hadn't got around to actually telling the world when General Ripper ordered his bombers to attack.
 * In the third Saw movie.
 * The premise of Crimson Tide basically deals with this possibility on a government-wide level (see Real Life examples below).
 * In Ronin, Stellan Skarsgård's character does this when "negotiating" over the case. He has to call by a certain time, or the Russian's girlfriend will be shot by a sniper.
 * In Analyze This, mobster Paul Vitti declares that he wants to get out of the Mafia, so he's written down "a few things" about every other mob boss and put the documents in safe hands in case somebody decides to do him in.
 * In Speed, Dennis Hopper has a bomb wired to a dead man switch, so that if he is killed, his finger releases the switch and it goes off. He does this while taking the Love Interest hostage, since last time he tried this he was the victim of Shoot the Hostage.
 * The bus also has a sort of dead Man Switch in that the bomb will be triggered if anyone tries to get off.
 * Though that's because Dennis Hopper is watching the bus like a hawk, both inside and out.
 * The main trigger for the bomb is also a literal Dead Man Switch, activated if the bus drops below 50.
 * In Spawn, CIA director Jason Winn in the film version had a device installed near his heart that, if his heart ever stopped, would send a signal out to an automated system designed to release a devastating virus all over the earth. Oddly, even the "normal" members of the CIA are shown thinking that this was a good idea ("Now, no one will dare kill you, sir!). It apparently never occurred to anyone to think about what would happen if the guy got into a car crash or had a heart attack.
 * In I Robot, Dr. Alfred Lanning left behind instructions for Will Smith's character, Del Spooner, in the event of his death. His  near the beginning of the film sets in motion Del's investigation.
 * Terminator 2: Judgment Day - Inventor Dyson makes a Heroic Sacrifice by standing between the escaping heroes and a pursuing SWAT team, hand-holding a heavy piece of wreckage over a detonator switch.
 * In Return of the Jedi, Bounty Hunter Boushh recommends that Jabba the Hutt pay higher than the listed price for Chewbacca, in light of the fact that "he's holding a thermal detonator!"
 * The Big Bad of Hancock is holding a dead man switch that will detonate a bomb attached to his hostages if his finger releases the trigger.
 * In Point Break, Bodhi tells Johnny Utah that if doesn't meet with another robber at a certain place, that robber will kill Utah's girlfriend.

Literature

 * Done several times in the Enderverse—Valentine threatens Peter with something like this in Ender's Game, and Bean and Petra are concerned that the Mad Scientist Volescu had one set up for after his capture, possibly triggering a virus to fundamentally change the human race. In a more heart-warming example, Sister Carlotta has a note prepared to be sent to Bean that will automatically be sent to him if she doesn't check in for a period of time. Considering that he only receives it after her death, he realizes that Carlotta cared enough for him to do something every day of her life.
 * Raven from Neal Stephenson's book Snow Crash is very large and deadly, but the reason why almost everyone gives him a wide berth is that if you were to somehow kill him, allegedly a trigger attached to his brain would set off the (very real) nuclear warhead attached to the sidecar of his motorcycle. No one wants to risk it.
 * In a slightly different example, Havelock Vetinari of Discworld fame installed multiple Gambit Roulette Dead Man Switches in the city of Ankh-Morpork which are neither magical nor mechanical, but political in nature, thus ensuring that a Discworld with him will be much better than a Discworld without him. However, he is also slowly taking the time to set up a proper police force and bureaucracy for the city, making sure that after he's gone, the city will still thrive.
 * In John Grisham's The Partner, the titular character had stolen millions of dollars from his law firm and fled the country. When mercenaries track him down and abduct him, his failure to call in to his co-conspirator puts into action an elaborate plan to locate and free him.
 * In the Star Trek: New Frontier book series, the Redeemers place a special virus in their priests' blood. Should that priest be slain by anything other than natural causes, the virus goes airborne and obliterates all life on the planet it's on.
 * In the Double Helix novel, the Big Bad knows the circumstances between Calhoun and his Dragon, but he also makes it abundantly clear that they're both on the same team now (Calhoun is deep undercover again.) Thus, he tells them that should one of them die, he'll immediately assume the other did it and kill him.
 * The short story A Brief History of Death Switches by David Eagleman, though the titular death switches are not of the revenge sort but rather the "communicating from the grave" sort.
 * Robert Heinlein's Between Planets. To prevent the ship "Little David" from being captured by the Federation, it has a bomb attached to a Dead Man Switch.
 * A better one is in The Long Watch features a man holding off a coup seeking nukes by placing them on a deadman switch. He hasn't the guts to kill himself and set them off and foil the coup that way, but if it only works if he's dead...
 * In the follow up to The Thrawn Trilogy it's established that Thrawn had a clone in his secret base who would be released a period of time without Thrawn's intervention. Although, given the period of time that passes... he obviously didn't put a great deal of thought into the delay.
 * Mavra in The Dresden Files had one set up in one of the books. She had evidence that Murphy had killed people (they were Renfields) and that Mavra was going to send that evidence to the cops. In Mavra's words, "I won't kill her. I'll unmake her." Dresden quickly comes to the idea of killing Mavra. Seconds later, Mavra tells him that, unless she says otherwise, the evidence will still be sent. So if she dies, there's no one to rescind the order. Fortunately, at the end of the book, Dresden makes up for it by threatening Mavra in an incredibly ballsy and spectacular way.
 * Every wizard is potentially one of these. When a wizard is dying they can unleash a Death Curse that will seriously mess up its target. The scope of the effect varies by the power of the wizard. Some Death Curses will just strip the killer of all their magical power (potentially lethal to another wizard or magical being) while others might destroy a few city blocks or an island.
 * In The Tomorrow Testament there was a confrontation where an alien whose scheme was uncovered asked what would prevent him from killing them all right away. The answer was that a big fleet moves to bombard his planet, and if they are dead no one else will be able to cancel the current order in time. There would be some repercussions, a lot of turmoil... but this will happen after the fact.
 * In the Stephen King novella Apt Pupil, Todd Bowden, while blackmailing Kurt Dussander, claims he left a letter (exposing Dussander) with a friend, to be opened and read in the event of his own death. Then when Dussander turns the tables and blackmails Todd, he claims that he left a complete account of Todd's actions in a bank deposit box, to be opened and read on the event of Dussander's death. They're both bluffing.
 * In Against a Dark Background by Iain M Banks, the Big Bad has rigged his dead man's switch to a whole network of bombs rigged destroy most of the critical infrastructure in the star system in which the novel is set, plunging it into (yet another) post apocalyptic dark age.
 * In Revelation Space Dan Silveste claims to have an antimatter bomb concealed in his tooth that will destroy everything within a kilometer if he dies or if his demands are not met.
 * In Ragtime, when Coalhouse and his allies take over the Morgan Library and rig it with explosives, it's mentioned that Mother's Younger Brother has the detonator set up so that it will be triggered if he (Younger Brother) is shot. (This being the early 1900s, this just means that he's sitting in such a position that he'll fall on it if he dies.)
 * In Dean Koontz's Frankenstein, Helios used several methods to ensure that his creations couldn't turn on him. One of these was a signal that would be sent out on his death, killing every one of his creations.
 * In the Prydain Chronicles the entire village of is protected by a magical version of this. Played with in that no one knows the "switch" even exists until an attack is attempted in the final book, since
 * In the Vorkosigan Saga book Cryoburn, a doctor who discovers a deadly secret about the cryo-preservation company he works for goes to outsiders for help, and is instructed to secure a copy of his information with a lawyer or a bank, to be released in the event that he dies or disappears or gets frozen. When the doctor gets caught by the company and dosed with Truth Serum, his Genre Savvy questioners get him to reveal this; however, he also reveals that two of the outsiders he talked to had taken copies of his information and made their own arrangements, giving the doctor's Dead-Man Switch some redundancy. And since the Corrupt Corporate Executives had, in the meantime, turned one of them into a Human Popsicle and killed the other one Deader Than Dead...
 * In Matthew Reilly's Area 7, the villian Caesar traps the President and his bodyguards in a remote facility, and has placed a transmitter on the President's heart. If his heart stops beating and the signal stops, dozens of nuclear bombs around America will detonate.

Live Action TV

 * The plot of The Outer Limits episode Dead Man's Switch revolves entirely around this trope.
 * In Robin Hood:
 * In the 1970s TV version of Captain America (comics), the superhero fights a villain trucking a neutron bomb for a terrorist plot by not only attacking the driver, but bending an exhaust pipe so it vents into the trailer to subdue any guards of the bomb. Unfortunately, when Cap investigates inside he finds out that the main villain was in there, is near death from his attack and he has a Dead Man Switch that would detonate the bomb if the villain's heart stops. Thus Cap and his Mission Control superior have to frantically apply first aid to prevent the detonation.
 * Turned Up to Eleven in Farscape: near the end of the series, John walked into enemy territory to negotiate wearing a portable nuke with Dead Man Switches "from every culture on my ship and a few cultures I haven't heard of," that would activate if his heart stopped, sped up, or if he got "too hot, too cold, too happy, too sad, thirsty, hungry, bored..."
 * The "too happy" was actually true, he had to tell his girlfriend not to stand too close to him because then the nuke would start beeping faster as his heartbeat sped up.
 * In Lost, the mercenary Keamy,  has one of these connected to his heart, set to trigger a large explosive in the event of his death.
 * In an episode of Babylon 5, Lennier saves the day through one of these. He programs the White Star's computer to immediately leave the area if he doesn't touch a control every few minutes. Sure enough, a   device starts screwing with everyone's mind, and the White Star is able to escape because he stops touching the control while under the influence.
 * In an earlier episode, a villain was threatening to blow up a station using one. The explosives were removed before the switch was released.
 * In the two part season one finale of Burn Notice, Michael plants various C4 charges around a nightclub owned by a heroin dealer and uses a detonator with a Dead Man Switch to force the dealer into giving him the information he needs to rescue Sam.
 * In an episode of SWAT, the boss of a bunch of crooks tries to escape by wiring himself to a bomb, with the switch in his hand. He demands and gets a truck, which he tries to escape in, driving one-handed. Naturally, something gets in his way, and he has to put both hands on the wheel - releasing the switch. Boom.
 * Percy in Nikita has one set where, should he die, it will send a message to the Guardians of all of the black boxes to release all of the information on the boxes to the public. The boxes are hard drives containing all of the illicit operations of the United States government for a long time. Should that information be released, it would tip the balance of world power. Because of this, Team Nikita is currently working on plan Gotta Kill Em All before launching an assault on Division HQ.
 * Percy later uses another variation of the same system. If he dies, his henchman Roan will receive the signal to immediately start a nuclear meltdown in the middle of Washington DC. As a second layer of protection, if Percy does not phone Roan by a certain time, Roan will also start the meltdown since it will mean that Percy has been captured.

Tabletop Games

 * Dungeons and Dragons
 * There are some monsters having this as an innate ability. E.g. gas spore reproduces this way: it'ss a fungal high-pressure bubble that floats toward warm-blooded animals, and when damaged explodes and showers everything around with its spores; any potential host may end up infected, then die, consumed by growing next generation of the fungus.
 * Draconians in Dragonlance are subjected to a magical effect upon death - depending on the subspecies, they turn to stone (if one is killed with a bladed weapon, it's likely to get stuck), dissolve into pool of acid or burst in flame, explode, or transform into ball lightning, which attacks and then explodes.
 * The classical spell contingency is built for this trope. A wizard can set their death as the trigger for pretty much any spell they have in their collection.
 * ...to the point that Forgotten Realms has the special kind of Undead called Blazing Bones which is created when someone protected by death-contingency is killed by fire while casting a spell.
 * AD&D2 dragon magic of Forgotten Realms includes 'Death Matrix' spell - when a dragon enchanted with it dies, it initiates a massive explosion loaded with scales, bones and dragonbreath. It's permanent and not dispellable.
 * D&D3.5 Complete Scoundrel introduced Fatal Flame - if the target dies before the spell expires, a mini-fireball explodes immediately, with the power dependent on Hit Dice. It's also useable offensively.
 * In Warhammer 40000, due to highly dangerous nature of the magicians (psykers), they are all shipped off to Terra where most of them are psychically fed to the Emperor and a few are trained to use their abilities for the Imperium. The places they're held at on their planets usually come equipped with a Dead Man Switch: If anything goes wrong, all the held psykers are instantly gassed. Considering what kind of trouble several hundred untrained and unsanctioned psykers can be, either on their own or as fodder for another entity (as in, without any warning daemons may try to use their bodies as doors into material world), this can be considered justified.
 * Also, the Imperial Infantryman's Uplifting Primer recommends shooting any psyker seen without his "honor guard" of three other guardsmen (whose main purpose also entails shooting him if he happens to show signs of unusual behavior - like having a tentacle grow out of his chest).
 * Let's not forget the Penal Troopers, who are convicted criminals given one last chance to serve The Emperor. They get to charge the enemy wearing explosive collars, with a commissar holding the detonator. If the bomb doesn't go off, they are absolved of sin and free to go. Of course, they are also standing in front of a hostile army, unarmed.
 * The new Space Wolves Hero Unit, Lukas the Trickster, has one of his hearts (ripped out by a Dark Eldar pirate, he survived) replaced with a stasis bomb- if he's ever killed, everyone around him (probably including his killer) will be trapped in stasis for eternity with his laughter.

Video Games

 * This trope is the crux of the plot of Splinter Cell: Pandora Tomorrow, if the big bad doesn't radio his henchmen and say "Pandora Tomorrow" the planned doomsday goes undelayed.
 * The first four Robot Masters you fight in Mega Man 7 were activated by a Dead Man Switch after Dr. Wily was sent to prison at the end of Mega Man 6.
 * The "Auto-" spells and effect materia in Final Fantasy games and inspired series work much the same way as Contingency in Dungeons and Dragons (useful when the Dean Man Trigger is set to bring the operator Back From the Dead).
 * Final Fantasy VI has a famous example with the Bonus Boss at the top of the Fanatic's Tower. If you manage to survive the incredibly lengthy staircase gauntlet (with no save points), and beat the boss, he'll cast Ultima before dying, killing the party. Fortunately, it was the game that introduced the Auto-Life spell to the series, which is the only way to win without excessive grinding or taking forever to drain the boss's MP to zero.
 * In Final Fantasy VII, the Final Attack materia is a linking materia to set up a spell or action when the character is killed. Linking either Revive or Phoenix to it pretty much guarantees immortality, as long as you have a way to keep your MP up (MP Absorb + Knights of the Round or Master Summon is a good idea.) The number of uses is limited by the materia's level (at most 5), though.
 * The Hijacking mission in Target: Terror has the pilot held hostage by a terrorist with a Dead Man Switch that will trigger a bomb if you kill him. Shoot the remote to disable it.
 * And the painful thing of this is that the hijacking mission is
 * In Marathon, if a player has his fusion pistol charged when he is killed, it will discharge its blast, possibly killing from beyond the grave.
 * The Aftermath ability in Pokémon (Called Detonate in Japan) does damage to the opponent equal to one-quarter its Max HP when the Pokémon bearing the ability is KOed.
 * The Destiny Bond attack has a similar effect except that it KOs the opponent when the user is defeated if they don't switch out.
 * The various members of the Quirky Miniboss Squad in Metal Gear Solid 3 appear to have switches that blow up their bodies upon their deaths, presumably to prevent Snake from capturing them alive or acquiring any intelligence from their remains. The Fear's switch also comes close to being a Taking You with Me, as it also results in shooting out dozens of poisoned crossbow bolts.
 * in Metal Gear Solid 2: Sons of Liberty, the Patriots are holding Olga's child hostage, and if Raiden ends up dying before completing the mission, they'll kill her.
 * Inverted in the case of the nuclear strike; the President needs to both be alive and input his code hourly in order to activate it, and if he fails to put it in or dies, the launch sequence will be nullified.
 * The titular Peace Walker is this for the US government; a mobile nuclear launch platform with a top of the line AI capable of launching on it's own initiative if the chain of command is out of touch.
 * Big Bad Clement uses one of these in the finale of House of the Dead: Overkill. He uses a remote switch that will blow up the surrounding area, explicitly calling it the trope's title. However, he soon hands it over after revealing he wants to redeem his evil ways, which Isaac Washington uses later to blow him up.
 * In the first X-COM killed Cyberdisk units have a habit of blowing up (and taking out entire buildings with them). It requires some effort to kill them in such a way that they won't explode and thus leave Cyberdisc remnants for research.
 * Morgan in Syphon Filter 2 has a Dead Man Switch that will blow up the expo center if you shoot him before the bombs are defused. In the first game, killing Girdeux with explosives will set off the virus bomb.
 * In the final mission of Rainbow Six: Rogue Spear, Kutkin radios his Mooks every 2 minutes. If you kill any of them before taking him down, he will trigger the nuclear meltdown.
 * In Half-Life 2, whenever a Civil Protection Officer is killed, his radio emits a lout audible screech, followed by a female voice giving information on the location and officer's status, and ordering other nearby officers to respond.
 * In World of Warcraft, when adventurers kill the corrupted Titan Watcher Loken, he utters in his dying breath, "My death... heralds the end of this world." Loken was tasked by the Pantheon to imprison the Old God Yogg-Saron, and an "Algalon fail-safe" mechanism put in place to trigger if Loken met his demise. Unfortunately, the Titans didn't factor in the possibility of Loken's corruption by the whispers of the Old God that he was imprisoning. Hence, in the Ulduar raid instance, adventurers must "convince" Algalon that all is normal.

Subsequently, in Icecrown Citadel,.

Web Comics

 * In Girl Genius, a lone madman attempting to assassinate reluctant tyrant Klaus von Wulfenbach carries one of these, although it proves less effective than he'd hoped.
 * In Ask Dr Eldritch, the titular hero brings one on a mission to rescue his house troll.
 * In this Casey and Andy strip, it's revealed that Lord Milligan has explosives in his base triggered on his own heart stopping. He is a traditional villian, after all.
 * In General Protection Fault, Nega-Ki faces off against Ki's group as they're raiding the palace, telling them that she has a dead man's switch to flood the hallway with poison gas. Ki tells her counterpart that she's willing to die to save Nick, but questions whether her counterpart is willing to die to fulfill Nega-Nick's evil plans. Nega-Ki backs down, but moments later, soldiers arrive to capture Ki's group.
 * Sam and Fuzzy got succession rules for that.

Western Animation

 * In the Batman Beyond episode "The Final Cut," the last surviving member of the League of Assassins blackmails Batman into protecting him from the villain who has wiped out the rest of the League by hiding a bomb in Gotham City, programmed to go off if he does not enter the proper code every twelve hours. It doesn't do him much good.
 * Brock Samson uses this as a security measure in Venture Brothers when he has surgery to remove H.E.L.P.er's head, stuck in his chest like giant annoying shrapnel after the explosive finale of season 3. He nonchalantly pulls the pin on a frag grenade, and sticks it in H.E.L.P.er's mouth. He didn't trust his Argentinian Back-Alley Doctor.

Real Life

 * British missile submarines had (and may still have) the "bolt-from-the-blue" procedure, in case Britain is destroyed by a surprise nuclear attack. This is referenced in the VX episode of Spooks: when each new Prime Minister enters office, he or she writes letters to the captains of the four Vanguard-class submarines, which are placed unopened in the safe (once the PM leaves, the letters are destroyed unread.) If the submarines lose contact with London, they perform a considerable number of checks (including checking whether they can still pick up the Today radio programme on longwave). Once they are convinced that Britain is no longer there, they open the safe. There appear to be (according to the Peter Hennessey book The Secret State, the source for this) four things that can be in there:
 * Go to Australia, if it's still there.
 * Put yourself under American command, if the US is still there.
 * Nuke Moscow or whoever actually launched the attack.
 * Use your own judgment.
 * The US presidential line of succession assures that there will be a Chief Executive (and more importantly, a Commander-in-Chief) at all times. This extends to making sure that during State of the Union addresses, one upper level cabinet member is far, far away from the proceedings, in case of a massive terrorist attack.
 * In some Pennsylvania prisons, guards are equipped with a distress radio that will call in reinforcements if they pull a rip-cord buttoned to their shirt, or if their torso tilts by more than 45°. Thus, if they get into a fight with an inmate and are incapacitated, the distress signal automatically alerts the entire facility.
 * Perimetr. Not an automated system, but a devolving of launch authority to lower-ranking officers. An earlier version was revealed (decades after the fact) to have been in place during the Cuban Missile Crisis. Soviet officers in Cuba had been given authority to use nuclear weapons in the event of a US attack. The authority was yanked after the U-2 shootdown.
 * A website called "You Were Left Behind" sells itself as a service for devout born again Christians who are worried about being taken up into heaven during the Rapture, and want to leave messages for friends and loved ones just in case it happens during their lifetime. The site works (or claims to work) by having a small inner circle of administrators who have to log in at least once every three days. If all of these brave Christian soldiers miss two updates in a row at the same time, then the Rapture must have happened and all the clients' messages will be delivered.
 * A similar all-purpose site exists, fittingly enough called Dead Man's Switch.
 * During the Beslan terrorist attack in Russia in 2004, the men set up dead man's switches so that if the terrorist were gassed, the bombs they set up would still go off.