How a Car Kill Switch Works

Cars in a line.

A car kill switch interferes with the car engine's combustion process and is engineered to shut it down in the quickest way possible. Depending on their design, different types of kill switches can stop the car through several different mechanisms. One of the most common ways involves the spark plug, and other methods can activate based on a certain number of engine revolutions.

Spark Plug

When a car kill switch interrupts the flow of electricity to the spark plug, the car engine’s combustion stops. While this is a popular method, it carries the risk of the car back-firing if there is a significant amount of gasoline vapors in the engine.

Engine Sensors

Some car kill switches have been developed with sensors that detect either a certain ratio from the spark plug, a certain RPM of the engine, or both. This has been proven a more effective way of shutting down the engine without the chance of backfiring or other damage.


Both types of kill switches are connected to the engine’s circuitry through a system of wires. When the switch is set to “closed,” the normal electrical circuit from the spark plugs can be finished. When the kill switch is opened, the electricity is blocked from causing the combustion that runs the engine.