An immobiliser or immobilizer keys is an electronic device fitted to an automobile which prevents the engine from running unless the correct key (or other token) is present. This prevents the car from being "hot wired" after entry has been achieved.
Immobilisers have been mandatory in all new cars sold in
The microcircuit inside the key is activated by a small electromagnetic field which induces current to flow inside the key body, which in turn broadcasts a unique binary code which is read by the automobile's ecu. When the ecu determines that the coded key is both current and valid, the ecu activates the fuel-injection sequence.
In some vehicles, attempts to use an unauthorized or "non-sequenced" key cause the vehicle to activate a timed no-start condition and in some highly advanced systems, even use satellite or mobile phone communication to alert a security firm that an unauthorized attempt was made to code a key.
Coincidentally, this information is often recorded in modern automobile ecus, which may record many other variables including speed, temperature, driver weight, geographic location, throttle position and yaw angle. This information can be used during insurance investigations, warranty claims or technical troubleshooting.
Add-on immobilizer keys are available for older cars or vehicles without factory immobilisers. The insurance approval for a self-arming immobiliser is known as "thatcham 2" after the motor insurance repair research centre in thatcham,