selector switch

Kill switch

A kill switch (also called an e-stop) is a security measure used to shut off a device in an emergency situation in which it cannot be shut down in the usual manner. Unlike a normal shut down, which shuts down all systems naturally and turns the machine off without damaging it, a kill switch is designed to completely abort the operation at all costs. Often, they are used to protect people from sustaining an injury or being killed, in which case damaging the machine may be considered to be acceptable.

Physical world applications

A similar system, usually called a dead man's switch (for other names, see alternative names), as its name suggests, is a device intended to stop a machine in case the human operator becomes incapacitated, and is a form of fail-safe. They are commonly used in locomotives, freight elevators, lawn mowers, tractors, jet skis, outboard motors, snowblowers and snowmobiles.


It is used to shut down vehicles and machinery if the operator loses control or is ejected. A common example of this would be the kill switches used by boaters wherein a cord connects the kill switch to the operator (usually by their life jackets), and if the operator is thrown overboard in an accident, the cord will pull the switch and immediately shut down the vessels' engine.

NASCAR (National Association for Stock Car Auto Racing) requires all their stock cars to be equipped with a steering wheel-mounted kill switch, in case the accelerator pedal sticks and the driver needs to shut down the engine.

Kill switches are also used on land vehicles as an anti-theft device and as an emergency power off.


A kill switch is also used for gasoline pumps or any other device that pumps large amounts of explosive or flammable chemicals. There is commonly a single kill switch for all pumps at a pumping station.

Musical instrument

An electric musical instrument, such as a guitar or bass guitar, may have a kill switch. It is used infrequently but most commonly in heavy metal music. Contrary to popular belief, a kill switch doesn't break the circuit but works by switching between the hot signal from a pick-up and the ground signal. A typical way of achieving this is (on a guitar with a volume control for each pick-up) by turning down the volume on one of the pick-ups then alternating the pick-up selector switch between that pick-up and one with the volume turned all the way up. They are sometimes used when a singer doubles as a guitar player and isn't playing or sometimes used as an effect during a song. Tom Morello of Rage Against the Machine and Audioslave, Buckethead ("Jordan"), and Ace Frehley of Kiss (such as in the intro to the song "Cold Gin" from the Kiss Alive! album) are well known for their use of the kill switch. Jack White uses a kill switch during some of his performances and in songs like Icky Thump. Some amateur guitarists fashion their own kill switches. These are usually very crude but still just as effective as one made by a professional.


Treadmills often use a safety key that the runner clips to his/her waist, and if he/she falls or trips, the safety key is pulled out, and the machine stops immediately.

In computer software

The concept of "kill switch" may also be applied to software as an "anti-piracy" feature, most notably in "Windows Vista" operating systems. It renders the software essentially useless to users running what is determined by the software author to be an illegitimately obtained, or "pirated", copy. In the example of Microsoft Windows, the company developed a verification tool named "Windows Genuine Advantage", that originally activated a kill switch on what Microsoft deemed to be an illegitimately obtained copy of the operating system. In effect, a software kill switch is acting like an electronic anti-theft system in cars, that disables a stolen car. However, these software kill switches have been shown to have varying degrees of success, as false positives have been known to occur, prompting some vendors like Microsoft to "turn off" the software kill switch in response to market pressure.

There is some anectodal evidence that some software vendors install kill switches in their software to enforce planned obsolescence, also known as a "forced upgrade". If this happens, it can, depending on the business situation of the affected customer, cause considerable disruption in said customer's business functions.

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