Dead man's switch

A dead man's switch is a <a href="/facts/Switch/vqbNDgYm">switch</a> that is designed to be activated or deactivated if the human operator becomes incapacitated, such as through <a href="/facts/Death/VJmq29qm">death</a>, <a href="/facts/Loss_of_consciousness/SS240v32">loss of consciousness</a>, or being bodily removed from control. Originally applied to switches on a <a href="/facts/Vehicle/jSIEqANL">vehicle</a> or <a href="/facts/Machine/Dq1W2kwI">machine</a>, it has since come to be used to describe other intangible uses, as in computer <a href="/facts/Software/RP79lVSW">software</a>.
These switches are usually used as a form of <a href="/facts/Fail-safe/bLhUUvL4">fail-safe</a> 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 <a href="/facts/Locomotive/C9YV7wrQ">locomotives</a>, <a href="/facts/Aviation_fuel/XGW64rro">aircraft refuelling</a>, <a href="/facts/Elevator/ug3nh0o8">freight elevators</a>, <a href="/facts/Lawn_mower/sVtTfejM">lawn mowers</a>, <a href="/facts/Tractor/gNc7kb4a">tractors</a>, <a href="/facts/Personal_watercraft/QKs5N8DJ">personal watercraft</a>, <a href="/facts/Outboard_motor/4TjsuNRN">outboard motors</a>, <a href="/facts/Chainsaw/ndhINGwe">chainsaws</a>, <a href="/facts/Snowblower/jEBq8ev6">snowblowers</a>, <a href="/facts/Treadmill/otD1JJuP">treadmills</a>, <a href="/facts/Snowmobile/0Gue0xhN">snowmobiles</a>, <a href="/facts/Amusement_ride/agnm0DMj">amusement rides</a>, and many <a href="/facts/Medical_imaging/pL6JyJEp">medical imaging</a> 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 <a href="/facts/Fail-deadly/pENDtlaJ">fail-deadly</a>, 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 <a href="/facts/Special_Weapons_Emergency_Separation_System/usgbalyV">Special Weapons Emergency Separation System</a> is an application of this concept in the field of nuclear weapons. A more extreme version is Russia's <a href="/facts/Dead_Hand/hEv0H8A7">Dead Hand</a> 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.
A similar concept is the handwritten <a href="/facts/Letters_of_last_resort/fdos294W">letters of last resort</a> from the <a href="/facts/Prime_Minister_of_the_United_Kingdom/Uf40UlBb">Prime Minister of the United Kingdom</a> to the commanding officers of the four British <a href="/facts/Ballistic_missile_submarines/Alykksc1">ballistic missile submarines</a>. 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 <a href="/facts/Vault_7/QEe6KueH">Vault 7</a>.
A related device is a <a href="/facts/Kill_switch/oymcV71g">kill switch</a>.

Dead man's switch open-in-new

Dead man's switch