A dead man's switch (for other names, see alternative names) is a switch that is automatically operated in case the human operator becomes incapacitated, such as through death or loss of consciousness.
The switch, a form of fail-safe, is usually wired so that it stops a machine by breaking a series circuit, although a spring-operated "dead man's switch" can be used to activate a system by completing a circuit when it is no longer held down (as in some explosive vests detonated by suicide bombers). Switches of the former type are commonly used in locomotives, aircraft refuelling, freight elevators, lawn mowers, tractors, personal watercraft, outboard motors, chainsaws, snowblowers, tread machines, snowmobiles, and many medical imaging devices.
A dead man's switch may also be used to activate a harmful device, such as a bomb or IED. The user holds down a switch of some sort in their hand which arms the device. When the switch is released, the device will activate, so that if the user is killed while holding the switch, the switch will be released and the bomb will detonate (i.e. fail-deadly). The Special Weapons Emergency Separation System is an application of this concept in the field of nuclear weapons (see Dead Hand (nuclear war)).
A similar concept has been employed with computer data, where the "switch" is a decryption key that can release sensitive information, as with the WikiLeaks "Insurance File".
Read more about Dead Man's Switch: Background, Vigilance Control, Alternative Names, Event Recording
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