A kill switch, also known as an emergency stop (e-stop) and as an emergency power off (EPO), is a safety mechanism used to shut off machinery in an emergency, when it cannot be shut down in the usual manner. Unlike a normal shut-down switch or shut-down procedure, which shuts down all systems in order and turns off the machine without damage, a kill switch is designed and configured to abort the operation as quickly as possible (even if it damages the equipment) and to be operated simply and quickly (so that even a panicked operator with impaired executive functions or a by-stander can activate it). Kill switches are usually designed to be noticeable, even to an untrained operator or a bystander.
Most kill switches feature a mollyguard, a removable, protective barrier against accidental activation (e.g. a plastic cover that must be lifted or glass that must be broken). Kill switches are features of mechanisms whose normal operation or foreseeable misuse might cause injury or death; industrial designers include kill switches because damage to or the destruction of the machinery is less important than preventing workplace injuries and deaths.
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 (or activate one) if the human operator becomes incapacitated, and is a form of fail-safe. They are commonly used in industrial applications (e.g., locomotives, tower cranes, freight elevators) and consumer applications (e.g., lawn mowers, tractors, personal water craft, outboard motors, snowblowers, motorcycles and snowmobiles). The switch in these cases is held by the user, and turns off the machine if they let go. Some riding lawnmowers have a kill switch in the seat which stops the engine and blade if the operator’s weight is no longer on the seat.