Destruction Equals Off Switch

The reasoning behind an Overclocking Attack—when a control console is destroyed, anything that it controls is automatically switched off.

This of course makes little sense when you think about it. Try switching your radio on, then pulling off the tuning knob. All you end up with is your radio stuck on whatever station you tuned it into. Every system should remain stuck like this after the control console is destroyed, but it never is.

This even happens with systems where it would make little sense to turn it off upon destruction. Why would you include a fail-safe that automatically- for example- lowers the shields of your starship when the console that controls the thing defending your starship is destroyed? And why wouldn't aforementioned vital system not have a secondary control console somewhere, or at least a Shield Dimmer Switch?

Ironically, the only systems that don't do this are usually also the ones that will cause a disaster if they can't be shut down, such as the main reactor.

It never sets off an alarm, either. Destroying an Insecurity Camera doesn't trigger some kind of automatic defence system, facility-wide alert or even notify the janitor. It just turns off the camera. Apperently nobody is watching the monitors for these cameras either, since they don't seem to notice when one suddenly goes offline.

This is most often a major flaw of the Big Bad's Doomsday Device and/or Supervillain Lair. But even the good guys fall victim to this with their extremely poor McGuffin-guarding security systems. Most often goes hand-in-hand with Computer Equals Monitor and Made of Explodium.

Not to be confused with Inventional Wisdom, where a literal switch brings about destruction of idiotic proportions.

Examples of Destruction Equals Off Switch include:

Anime and Manga

Subverted on Yu-Gi-Oh! GX: Kenzan catches Saiou's Brainwashed minion after he has used a laptop to fire a missile from a Kill Sat, so he figures the best way to fix things is to destroy the laptop. It's not until after he's done so that someone tells him he's in fact destroyed the Off Switch. Did we mention Saiou is Dangerously Genre Savvy?
Something similar happened at the end of the Virtual Nightmare arc of Yu-Gi-Oh!—by destroying the console, Marik unintentionally destroyed the off switch.
Used at the end of the A Certain Scientific Railgun anime, where the unpowered Ruiko Saten smashes the consoles controlling the Big Bad's psychic-power-limiting device, thus allowing her friends to use their powers and defeat the villain.

Film

Averted in Star Wars. When Luke and Leia are being pursued by Stormtroopers on the Death Star, Luke shuts a blast door and destroys the console specifically to make it harder for them to open the door again. Unfortunately the controls for the bridge they needed were on the same panel...
- The same movie plays it straight a few times as well. For instance, in the same exact scene. Why are the controls to the door only on one side of the door?
- Played straight in The Phantom Menace where the destruction of the droid control ship causes the entire army of battle droids to shut off, and even fall apart.
  - The Droid Control Ship is given justification in the expanded universe: the droids stopped working because the Trade Federation was too cheap to outfit all the droids with processors, as well as being paranoid about them be used against them. The droids fell a part because they are held together magnetically. The stupidity of this was noted, and most of the droids used in the Clone Wars had central processors.
Used in the James Bond movies Diamonds Are Forever and Die Another Day.
Averted in The Incredibles; in fact, it's the Omnidroid itself seeking to destroy its remote control, so it cannot be controlled by anyone else, and it's up to the Incredibles to try keep it safe until they can figure out how to operate it.

Live Action Television

Happens many times on the various Star Trek series with force fields. Numerous episodes have characters shoot a control panel and a force field shuts off. Why even bother having access codes to unlock??

Radio

Used as a last resort at the end of the Novacom arc of Adventures in Odyssey: Novacom blocked all methods to stop the uplink of their Mind Control radio waves. Although Whit and Tom find the machine, they can't turn it off; fortunately, the uplink is connected to a machine Novacom stole from Whit, and he stops it by making it self destruct. In this case, they were at least racing against a countdown and knew they had to destroy the machine before it sent its signal—destruction could prevent the operation from executing, but not turn it off if it started.

Video Games

Security cameras suffered badly from this trope in both System Shock games. Blowing them up reduced the security of a level, rather than set off the alarm.
- Same in Spiritual Successor BioShock (series), but come on: the system were made in the Fifties. Electronics in Rapture appear to run off of an electrified gel that runs through tiny pipes instead of actual electricity going through wires. Basically, they're what Descartes thought our nervous system was.
Averted in the First-Person Shooter series No One Lives Forever. Shooting cameras sets off the alarm.
- Same with Alpha Protocol.
Dead Space
In Ghost Trick, a power failure caused when the electric chair that was being set up to execute Detective Jowd malfunctioned and exploded opened the doors of all the cells in the prison, setting the prisoners free. This is Handwaved a few moments later, as you're told it's a security measure.

Western Animation

Averted in Teen Titans, in which Raven and Terra are arguing whether to destroy a control panel in order to shut off a device that's going to destroy the tower if they don't stop it. It ends up getting destroyed... which makes the device go faster.

Terra: Okay, maybe smashing the computer was a bad idea...

Hilariously averted in The Batman - Batgirl sabotages the doomsday device, the countdown stops...

Villain: What happened? Did we lose power?
Henchman: No, the countdown timer's disabled. The device is still operational.

The Real Adventures Of Johnny Quest has a particularly egregious case in the final episode. When the crew use Questworld to track down a reality warping demon, it takes over the system, leaving Johnny trapped. His father saves him by taking an axe to the laptop. Never mind that based on everything established about Questworld so far, a stunt like that could potentially kill anyone connected.

Real Life

Brake systems can work either way. In most passenger cars, any serious problem will cause the brakes to "fail open" and be unable to stop the car, because the system depends on hydraulic fluid reaching the pads to close them. But in locomotives and large trucks, the air brakes are designed so the system actively works to keep the pads open, which means any problem causes them to "fail closed" and bring the vehicle to an immediate stop.
These systems exist today. It's in the best interest of certain devices to "fail-open" or "fail-closed" in order to prevent damage to other connected devices. If power is lost to electronically controlled water valves, the valves may either "fail-open" or "fail-closed" (depending on the system) to protect the systems that they service. Likewise, electronically controlled steam valves have to "fail-open" so that steam pressure doesn't build up and rupture the pipes.
- And simple secondary fail-safes are placed, usually being as simple as possible, in case of any kind of primary failure. For the steam pipe example, a burst disk that can only withstand a certain amount of pressure, a spring-mounted pressure valve where the steam pressure escapes when greater than the spring tension, or a thermal relief valve that uses a metallic rod that lengthens when heated to raise the valve cap.
Many functionally hot-pluggable buses aren't supposed to be, and in older computers yanking a keyboard cable (for example) could damage the motherboard. ROM cartridges are particularly risky, as apart from the ZIF socket on the original NES, most could easily damage the system from a voltage spike if a cart was removed. (It is not unheard of, however, for the truly inept to even try to hot-plug ISA or PCI cards, or even RAM modules. Disaster is occasionally averted, but even when the poor shlub gets lucky a reboot is usually required.)
A classic power switch works by bridging the connection when it's on. Most methods of destruction would leave a gap in the connection where the power switch used to be, thus disabling the device. Which is usually a lightbulb. A lot of work just to turn out the lights, isn't it?