Dead man's switch
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- For other uses, see Dead man's switch (disambiguation).
A dead man's switch (also known as - mainly in Britain - as a dead man's handle) is a device intended to take some action if the human operator becomes incapacitated in some way, a form of fail-safe practice. Because the action is usually to slow down or stop a vehicle, this is also sometimes known as a dead man's brake.
For example, most freight elevators, lawn mowers, jet skis and snowblowers in some countries use a dead man's switch or a similar mechanism, causing them to respectively stop closing the elevator door or shut down if the switch is released. If a person faints while mowing the lawn, their hands will relax and the mower will shut off.
A very common use is in a locomotive; for that use, see dead-man's control.
Software versions of dead man's switches are used (usually only by technically competent people, and not many of those) to perform such tasks as notify friends or delete or encrypt data. The non-event triggering these can be almost anything, from failing to log in for a week consecutively, to not responding to an automated email ping, to a GPS-enabled phone not moving for a period of time, or even just failing to type the right magic sequence within a few minutes of the laptop booting. The motivations vary depending on the individual needs. Someone in a police state may be much more concerned about locking up their data securely (or deleting it) while others may just wish to alert friends or the authorities by email that something may be amiss.
Dead man's switch devices have also been used in suicide bombing, to trigger the explosive if the bomber is shot or overpowered. This is a fail-deadly mechanism, rather than a fail-safe mechanism.