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The Time Bomb is one of the tropes popular in all forms of film and TV writing, as it adds a sense of urgency to the story — whatever the characters must do, they must do it within the time limit or the bomb will go off (the hostage will be killed, the poison will be released...).
The hero will succeed in their task onlywithin a few seconds of the deadline - especially if there is an actual digital readout involved, counting down the seconds until Sudden Doom. If the hero is James Bond, the time remaining when the clock stops will, of course, always be 0:07. For other heroes, three seconds and one second seem common. (There's even the movie Canadian Bacon, where the clock's stopped at .7 seconds.)
Often there's the illusion of Real Time when we see the timer, but if you count the seconds and watch the clock, a 30 second countdown can often stretch as long as two minutes. Or it may ramp up and tick off far more time than has passed. (See Magic Countdown.)
In many cases, the bomb will not go off until one or two seconds after the timer reaches zero, even though the timer itself had tenths- or hundredths-of-a-second precision.
There are also rare instances where the bomb isn'tdefused: instead, it is made so that the explosion doesn't affect anyone (except maybe the bad guys). If this happens, there will be an Outrun the Fireball moment.
This trope is actually in contrast to real-life bombs which are camoflagued and seldom, if ever, include a visible timer. Television bombs must include a countdown to add tension, and often include blinking lights to let the audience, and the heroes, know that it is a bomb they are looking at.
There would probably be a lot more dead TV heroes if the villains would stop putting blinky lights and timers on their bombs.
Summer Wars: Love Machine eventually sets a two-hour countdown on OZ's worldwide clock. When it hit zero, it was supposed to crash a Japanese satellite, which it had recently taken over, to crash into a nuclear power plant. Once Love Machine is thwarted, and the timer stops, it starts up again, this time with the satellite aiming right at the house the main characters are sitting in.
In one episode of Neon Genesis Evangelion one of the Eldritch Abominations has taken the form of a microscopic parasite that infects the organic components of the Elaborate Underground Base and spreads into the main computer to trigger the Self-Destruct Mechanism. Ritsuko climbs inside the computer core to make modifications that would prevent this, but is soon running out of time. With only 10 seconds left, Misato say that they've lost, to which Ritsuko replies that that's even one second more than she needs.
The Digimon movie "Our War Game" had the clock stop with it fluctuating at .01 and .02 seconds. However, this was about five seconds before the missile landed and destroyed Tokyo
In Excalibur, team enemy Gatecrasher devises an...unusual example: as Excalibur is making breakfast, one of the eggs jumps off the counter, breaks open, and reveals a cartoony bird who starts shouting at the team. As they stare at it in complete bogglement, it starts counting down...
Speed has fun with the fact it's not a time bomb, but a speed bomb, so the speedometer acts as a readout meter. When the bus encounters a problem, director Jan De Bont likes to show the speedometer getting ohsoclose to the 50-mph point.
Galaxy Quest subverts this beautifully when the characters defuse an overloading reactor with about 20 seconds to spare...but to their consternation the countdown keeps going till it reaches 1 and stops. They then comment, relieved, that "it always did that on the show" the real ship was based on.
Subverted in The Naked Gun 2 1/2: an attempt to stop the bomb actually increases the rate of countdown. When all is lost, the fleeing hero trips over the power cord, deactivating the bomb.
The Simpsons Movie. Homer actually causes the timer to advance when he kicks the bomb dejectedly. In another scene, a bomb defusal robot shoots itself with Chief Wiggum's gun, in a scene similar to one from Full Metal Jacket.
Subverted in Lethal Weapon 3: a foolhardy attempt by Riggs to defuse the bomb speeds up the counter. The only thing left to do is run, and let the building be destroyed. On a related note: why do the heroes never, ever just pull the detonators out of the plastic explosives?
In Diamonds Are Forever Mr. Wint and Mr. Kidd used timed bombs (without visual counters) twice - first to destroy the diamond-smuggling helicopter, and at the end in an attempt to kill Bond and Tiffany Case.
The bundle of explosives in The Mask, which The Mask disposes of by swallowing it.
In the novel, it was 34 seconds, to which Dr Hall says "Plenty of time. Hardly even exciting." But not to the people still stuck on Level V; "... to improve the subterranean detonation characteristics of the atomic device, all air is evacuated from Level V, beginning 30 seconds before detonation." Hall's response: "Oh."
In the The Shadow movie starring one of the Baldwin brothers there is a nuclear device (in a Pre-World War II 1930's setting America) which was going to blow up in 13 hours or something similar, but of course tampering with it trying to shut it off lead to ... 0.1 seconds left on the timer. Hooray!
Disney's Peter Pan. The bomb Captain Hook leaves for the title character, which is set to go off at 6 o'clock.
Stargate: One of the most egregious Magic Countdown examples, as O'Neil says they have five minutes to activate the Stargate and leave. However, once he cues up the Digital Readout, it counts down at a rate of about two seconds per actual second.
1986 movie The Manhattan Project. The radiation from the home-made nuclear weapon causes its own electronic timer to count down with increasing speed. It is finally stopped, reading 7:16:45, which refers to the date, July 16th, 1945, of the first atomic bomb test detonation.
John Woo's Broken Arrow. Hale jumps off the train pressing the cancel button on the remote trigger exactly at two seconds.
In Armageddon, this happens not once, but twice in a row. The first time, the timer on nuclear bomb is remotely canceled from Earth, only to be restarted after a direct order from the President. Back on board the asteroid, the bomb is stopped again manually, the timer freezing at 2.46 seconds.
Face Off. Castor Troy (as Sean Archer) casually disarms his own bomb with 2 seconds left on the clock.
In the British disaster film Juggernaut (aka Terror on the Britannic), an extortionist puts 6 identical , booby-trapped bombs on a cruise ship, promising the plans to defuse them if a ransom is paid by dawn tomorrow. Cue Richard Harris para-drops in to try to defuse them.
One is found strapped to a man in The Hurt Locker. This is one of the rare cases where it can't be disarmed, and the man (who claims he was forced to wear it, and is not a terrorist) is killed.
The Fifth Element has one in the hotel room. Somewhat subverted, in that the heroes take a moment to decide whether or not they can disarm it, then decide to just run away from the thing. The villain who set it up does disarm it with five seconds on the timer. Then one of the aliens he pissed off earlier arms his own - starting with a five second timer. Presumably just so that anyone who saw it when it was activated would have time to soil themselves before they died.
In Detective Conan: The Private Eye's Requiem, Conan must deactivate the wristband bombs attached to Ran and the kids which will set off at the clock's hour or if they exit the amusement park's boundaries. He needs to input the correct computer password, accomplishing it, and successfully resets the timer with 9/10 of a second to spare.
In the Saw franchise almost every trap has the classic timer attached. Subverted in that the the victim is usually about 3 seconds away from defusing it when it goes off. Justified in the sense that the series would have very little following if people actually got out and the devices never went off while being close increases tension and their attempts to get out typically provides the torture portion of the "torture porn".
Mater gets one strapped to his air filter during the climax of Cars 2.
The Nostromo's Self-Destruct Mechanism in Alien counts, since it gives Ripley only ten minutes to leave the ship before it explodes. She makes it out just in time, including stopping to pick up the cat, and discovering and mercy-killing her cocooned crewmates in the director's cut and novelization.
In Heathers, the heroine tries to prevent her high school from being blown up by a time bomb.
A throwaway bit in Heinlein'sStarship Troopers involves a talking time bomb. Rico jumps into a building full of Skinnies, throws something at them, and jumps back out. It begins yelling at them in their language: "I'm a thirty second bomb! I'm a thirty second bomb! Twenty-nine... twenty-eight..." The explosion is not described.
The second season opening episode of War of the Worlds, in which the base of the Blackwood Project was blown sky-high.
An episode of Robocop The Series involved the title character having to dispose a nuclear bomb in the OCP building, having to align two triangle-shaped switches into an hourglass. This is accomplished with (you guessed it) one second to spare.
Subverted in NCIS, where a military bomb disposal officer confidently proclaims that he has several minutes to defuse a bomb, which promptly blows up in his face in a cloud of dust a laUnwinnable Training Simulation. His training officer then explains that one should never assume the timer on a bomb is accurate and smugly comments that "the bad guys watch movies too."
Subverted again in a different episode when Gibbs finds a bomb under a bed in the house they are investigating. The team races out of the house and dives to hide behind a car. Over an hour later the bomb goes off just as the ME arrives to ask what they're all doing sitting there.
Honorable mention to the fireworks O'Neill threatens his SGC recruits with during a training exercise in "Proving Ground". The recruits can't figure out how to disarm the "bomb" before the timer goes off, so the team leader aborts the exercise.
Then, there's the episode "Fail Safe". In an attempt to destroy/divert an asteroid headed towards Earth, SG-1 places a bomb on it. Unfortunately, Carter then discovers that the asteroid itself is Made of Explodium, and their bomb will trigger an explosion large enough to destroy Earth. With only a few minutes to go before the timer reaches zero, the team climbs back out to their bomb, only to discover that the control mechanism has been damaged by a falling rock. To make matters worse, instead of the classic red-wire, blue-wire, it turns out that all of the control wires are the same color; as O'Neill puts it, "This is a very poorly designed bomb!"
In an early episode of Sledge Hammer!, Sledge has to find and disarm a time bomb hidden in a clock store.
The "MacGruber" skits from Saturday Night Live, which are themselves a parody of MacGyver, always take place in a locked room with some sort of time bomb. One of his allies (Maya Rudolph, later Kristen Wiig) is always on hand, counting down the time on her watch. However, the bomb always ends up exploding.
In the Star Trek: The Original Series episodes "Obsession", "The Immunity Syndrome" and "The Doomsday Machine", the bomb was used by the Enterprise crew to destroy a Monster of the Week. In each case crew members or the Enterprise had to get out of the blast radius before the bomb detonated.
Leoben claims to have planted one in the first season of Battlestar Galactica, but he's a perpetual liar who loves to Mind Frak people.
A common plot device in Hogan's Heroes, although in this case it's usually the heroes who set the bomb. Much drama comes of having to escape the area before it goes off and much comedy comes of Carter's bombs going off a few seconds later than his eager countdown.
Played straight more than once in Chuck ("Chuck Versus the Intersect", "Chuck Versus the Sandworm") but also subverted, as Chuck and Sarah encounter a large device with a countdown timer that they believe to be a bomb. After an unsuccessful attempt to defuse the bomb, as the timer nears zero, they share a Now or Never Kiss, but the device turns out not to be a bomb. All three of those in the first nine episodes of the series. Also played straight in "Chuck Versus the Third Dimension", in which the device has to be taken away from the crowd.
Buffy the Vampire Slayer had a time bomb in "The Zeppo" built by undead school sociopath Jack O'Toole - in a game of chicken, Xander convinces Jack to disarm it, pointing out being undead wouldn't be as much fun in little pieces.
And then Angel had an ep actually named 'Time Bomb', where the team had to drain some of Illyria's power before she blew the whole world sky high.
Doctor Who had the Reality Bomb in "Journey's End", built by Davros and his new army of Daleks.. When detonated, it would turn all forms of matter into dust, the dust into atoms and the atoms into nothing, effectively cleaning out the entire universe and all parralel dimensions. Thank you, Doctor Donna, for stopping it.
Also in the First Doctor adventure "The Daleks"- the Daleks attempted to detonate a neutron bomb on Skaro in order to increase radiation levels on the planet and allow them to survive outside their city (wiping out the other native race, the Thals, in the process). The countdown is stopped with just a few seconds remaining.
Truth in Television subversion: On Build It Bigger, the host accompanies an excavation-crew in Peru as they set up explosives to expand a tunnel in the Andes. After lighting the fuse and retreating to a safe distance, their foreman shows him the 8-minute countdown that's running on his cell phone, which indicates there are about four minutes left before the blast. The explosives go off prematurely while they're filming this scene.
Danger: UXB, being about a Bomb Disposal unit during World War II, is a more realistic portrayal of this trope. The Germans keep dropping bombs with timed detonators because they know they'll cause more disruption and panic. Naturally no-one knows when the bomb will go off. An exception is in "Seventeen Seconds to Glory" when a naval mine is being defused. Once the timer starts they explode in seventeen seconds regardless. The naval officer drops the tiny device used to deactivate the timer — and at that point the timer starts whirring. While the man with him runs like hell, the officer scrabbles desperately in the rubble for the device. He's able to find it at the last moment.
Castle: "Countdown" has a dirty bomb with a timer set to go off in New York. Castle and Beckett find the bomb with less than 2 minutes. They send a picture of the bomb to an expert, but he can't see any way to disarm it in time. Castle and Beckett brace for the explosion, only for Castle to yank all the wires with the timer reaching 0. No boom, averting the Wire Dilemma trope.
In the episode "Still", a crazy guy sets a booby-trap for someone in his apartment, which Beckett accidentally steps on, and then proceeds to commit suicide in his cell. The bomb defusal team discovers the trap is basically immune to being defused, and also has a timer that will trigger about half an hour from then - the only way to stop the explosion is to guess the 5-digit number to the guy's detonation switch. Which of course they do, with like 3 seconds to go.
The NickelodeonGame ShowThink Fast featured one in the first version of its "Locker Room" Bonus Round. While being given 30 seconds to match items or characters behind lockers, the first contestant had to open the locker containing the Time Bomb in 20 seconds; otherwise, the second contestant would only be given 20 seconds (instead of 30) to find the remaining matches.
Done and re-done in the 2D Metroid series, where at the end of each 2-D game (and at the beginning of Super Metroid) to boot, where after the Big Bad is defeated, Samus has 5 minutes of Real Time to escape wherever she's in before a time bomb explodes. Always followed by an Outrun the Fireball moment as we see Samus' ship escape the explosion with seconds to spare, regardless of how much time was actually left on the clock.
They pulled that same trick in Metroid: Fusion where you think that after beating the SA-X silly, you set off the bomb yourself that you're homefree. Nuhuh. One little old Metroid escaped and... has grown into an Omega.
Splinter Cell: Pandora Tomorrow had an interesting example. A bomb set to release GM smallpox into the ventilation in Los Angeles Airport has only a few minutes left on the timer, not enough to defuse it or get it anywhere containable. Sam's solution? Carry it into the main terminal building and just leave it lying on the floor. The bomb squad gets called in and they contain the blast Just in Time.
In Illusion of Gaia you fight That One Boss, the vampire couple, with one of your best friends strapped to one!
Call of Duty games feature this trope in multiplayer. In Modern Warfare, planting the bomb involves opening up a briefcase filled with stacked C4 and punching in a code on a cell phone (whose screen is covered with a sticker that says BOOM.) World At War, the bomb is a few blocks of explosive, and is armed by winding a key several times, much like a clock. In both cases, the timer is always 30 seconds, with no way to change it. Also, disarming the bomb seems to be as easy as doing the exact same thing as arming it - and performing that action a third time will rearm it with the timer reset, ad nauseum.
Subverted in the beginning of Halo 2. You can take as much time as you want, but when you reach the bomb and killed all the aliens protecting it, a cutscene starts that has the Master Chief hurrying to the bomb and getting Cortana into the bombs computer.
In Syphon Filter, the first level of the first game has you racing to disarm one at the bottom of a subway station. The second level of the game has you trying to get out of the same subway station after you fail to stop the bomb.
In Police Quest II, Sonny had to diffuse the bomb in the bathroom of an airplane that the hijackers took control. With the bomb instructions, you have to cut and connect the wires in reverse.
In The Godfather: The Game game, you can carry a number of these. They are mainly used for building demolition.
The central premise of the Intellivision game Bomb Squad.
Played with during the limited-time world event in World of Warcraft to recapture Gnomeregan. As a last-ditch effort to halt the counter-attack, the villain activated a time bomb with a lengthy timer. The lead NPC cheerfully noted it was more than enough time to deactivate the bomb... until the villain, griping about factory settings, reset the timer to a few seconds.
The characters who participate in the Nonary Game in Nine Hours, Nine Persons, Nine Doors have a small explosive inside their digestive tract. The detonator starts counting down from 81 seconds after going through a numbered door, and the people who walked through the door must deactivate it within the time limit, else the bomb explodes. The Ninth Man learned it the hard way by going through the numbered door solitarily.
The Flash games Four Second Fury, Four Second Frenzy, and Four Second Firestorm are all a bunch of microgames in which you have four seconds to perform some task. One of the microgames is a time bomb with an averted Wire Dilemma - you are told which wire to cut. Still, four seconds on the timer.
Some games in the classic Mega Man series use these as platforms, the countdown being triggered when Mega Man jumps on them. Fortunately, the explosion is barely larger then the platform itself.
In the fifth game of the Mega Man X series, a multitude of these can be found in Spiral Pegasus/The Skiver's level, giving you only a few seconds to destroy them before they detonate in a screen-filling explosion that'll remove most of your health.
The Handy viruses in the Mega Man Battle Network series use these as their sole method of attack, giving you three seconds to destroy the bomb before it detonates in an unavoidable explosion. The same bombs can be used a weapon by Mega Man once the appropriate battle chip is earned and are a very convenient way to delete viruses. They can even be combined together to create an even stronger bomb (Just make sure it doesn't get pushed back onto your side of the field).
The SNES video game  (Rushing Beat Shura in Japan) has a time bomb near the end of the "airplane" part of the Alan Bradley Airport stage. You must destroy the plane's controls within 15 seconds or the bomb will explode causing the plane to crash. If the plane does crash, you'll be forced to go through the streets instead of Ozymandias Island.
SF Debris noted that a time bomb used by Janeway would've neatly solved the final moral conflictnote Blow up the space station so the Kazon can't use it on the Ocampa, or use it to get home and leave the Ocampa to their fate? of Star Trek: Voyager's series premiere. Of course if Janeway had thought of it, they wouldn't have had a series.
In the Futurama episode "A Big Ball of Garbage" the gang installs a time bomb on the giant garbage ball set to blow up in 25 minutes. Unfortunately, the timer was installed upside down, so it is actually set for 52 seconds.
Semi-lampshaded in the Justice League episode "Wild Cards", where the Joker plants twenty-five time bombs all over Las Vegas, challenges the league to find them, sends the Royal Flush Gang to stop them, and sets the entire thing up as a reality show, complete with actual timer on the screen.
Subverted: The league finds most of the bombs, but two go off:
The Joker manually detonates one and nearly kills Green Lantern.
The other one, the final one, is grabbed by the Flash and moved to the desert while it's going off.
A Batman The Animated Series episode involved the Clock King using a portable device to slow down time so he could sneak in and plant a bomb. Batman winds up grabbing the bomb, slowing time down and driving it out of town. There's a nice shot of Batman holding the bomb as it detonates in super-slow motion.
The Mega Man cartoon had this a couple times, with Mega escaping or removing the bomb rather than defusing it.
An episode of Johnny Test introducing Mr. Mittens has a time bomb that would turn all of Porkbelly into cats in one minute. His butler, Albert, lampshades how bombs always have a timer and wonders why the other villains always put a timer instead of immediately detonating them. Mr. Mittens justifies his reasoning with his bomb that they needed the time to get them out of the blast radius and keep Albert human, so he can clean his litter box.
Including it just because it was so epic: in one script for the now cancelled The Flash movie, Vandal Savage declared he'd done this. If the Flash, the "Fastest Man Alive" couldn't find it in time, it would kill his wife. Flash checks literally everywhere for it, but couldn't find it in time, and had to escape, saving himself and not carrying her away. A few decades later, Savage offhand mentions: "What bomb? I used a rocket to blow up Wifey-Poo".