The immobilizer is an electronic anti-theft device. It is activated when the ignition key is removed and, together with the engine control unit, largely prevents unauthorized starting of the engine. The system uses a transmitter and receiver unit in the ignition key (transponder). Whenever an attempt is made to start the engine, it transmits a new code to the car’s electronics. The immobilizing is only cancelled if the key sends an authorization code. New encryption technology protects the system against electronically copied vehicle keys.

Note:
No system can provide 100% protection against theft. If thieves possess the necessary skill and determination, they may even be able to overcome the electronic immobilizer.