Kill switch

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An unprotected 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, tower cranes, freight elevators, lawn mowers, tractors, jet skis, outboard motors, snowblowers and snowmobiles.

Vehicles

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 vessel's 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. Such devices are often equipped into bait cars and set up so that observing police can trigger the switch remotely.

Machinery

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 (for example, "Jordan" and "Circarama" ), Ace Frehley of Kiss (such as in the intro to the song "Cold Gin" from the Kiss Alive! album and during his concert solos documented in numerous 1970s video bootlegs), and Jonny Greenwood of Radiohead 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 sometimes rather crude but still just as effective as one made by a professional.

Gym

Treadmills often use a safety key that the runner clips to his waist, and if he falls or trips, the safety key is pulled out, and the machine stops immediately. In other cases treadmills use a more traditional kill switch, often mounted towards the rear of one of the hand-railings.

In computer software

The concept of "kill switch" may also be applied to software as an anti-piracy feature, most notably in Windows Vista. 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, or reduced functionality mode, on what Microsoft's mandatory software's deemed to be an unlicensed copy of the operating system. Software kill switches have been shown to have varying degrees of success, as false positives have been known to occur^[1], prompting some vendors like Microsoft to "turn off" the software kill switch in response to market pressure.

There is some anecdotal evidence that some software vendors install kill switches in their software to enforce ^[2] planned obsolescence, also known as a forced upgrade. This can cause considerable disruption^[3] in said customer's business functions.

References

See also

• Emergency stop