Editing Dead man's switch (section)

{{Short description|Device that reacts to the loss of the operator}}
{{About|a safety device used on vehicles and equipment}}
[[File:Dodemansknop Linde.jpg|thumb|upright|A pedal acting as a dead man's switch in a [[aerial work platform#Vehicle-mounted|bucket lift truck]]]]

A '''dead man's switch''' is a [[switch]] that is designed to be activated or deactivated if the human operator becomes incapacitated, such as through [[death]], [[loss of consciousness]], or being bodily removed from control. Originally applied to switches on a [[vehicle]] or [[machine]], it has since come to be used to describe other intangible uses, as in computer [[software]].

These switches are usually used as a form of [[fail-safe]] where they stop a machine with no operator from a potentially dangerous action or incapacitate a device as a result of accident, malfunction, or misuse. They are common in such applications as [[locomotive]]s, [[Aviation fuel|aircraft refuelling]], [[Elevator|freight elevators]], lawn mowers, tractors, [[personal watercraft]], [[outboard motor]]s, chainsaws, [[snowblower]]s, treadmills, [[snowmobile]]s, [[amusement ride]]s, and many [[medical imaging]] devices. On some machines, these switches merely bring the machines back to a safe state, such as reducing the throttle to idle or applying brakes while leaving the machines still running and ready to resume normal operation once control is reestablished.

Dead man's switches are not always used to stop machines and prevent harm; such switches can also be used as a [[fail-deadly]], since a spring-operated switch can be used to complete a circuit, not only to break it. This allows a dead man's switch to be used to activate a harmful device, such as a bomb. The switch that arms the device is only kept in its "off" position by continued pressure from the user's hand. The device will activate when the switch is released, so that if the user is knocked out or killed while holding the switch, the bomb will detonate. The [[Special Weapons Emergency Separation System]] is an application of this concept in the field of nuclear weapons. A more extreme version is Russia's [[Dead Hand]] program, which allows for either automatic or semiautomatic launch of nuclear missiles should a number of conditions be met, even if all Russian leadership were to be killed.<ref name="Fresh Air">Terry Gross & David Hoffman, ''Fresh Air'', [https://www.npr.org/templates/transcript/transcript.php?storyId=113579843 "'Dead Hand' Re-Examines The Cold War Arms Race"] {{Webarchive |url= https://web.archive.org/web/20171015151313/http://www.npr.org/templates/transcript/transcript.php?storyId=113579843 |date=15 October 2017 }} 12 October 2009.</ref>

A similar concept is the handwritten [[letters of last resort]] from the [[Prime Minister of the United Kingdom]] to the commanding officers of the four British [[ballistic missile submarines]]. They contain orders on what action to take if the British government is destroyed in a nuclear attack. After a prime minister leaves office, the letters are destroyed unopened.

This concept has been employed with computer data, where sensitive information has been previously encrypted and released to the public, and the "switch" is the release of the decryption key, as with [[Vault 7]].<ref>{{Cite web |date=March 10, 2017 |title=WikiLeaks Password Is an Anti-CIA JFK quote |website=News.com.au |url=https://www.news.com.au/finance/work/leaders/wikileaks-password-is-an-anticia-jfk-quote/news-story/d6c1cc5385c4f1330bb87f1be2ecefa3 |access-date=2023-11-23 }}</ref>

A related device is a ''[[kill switch]]''.