A car immobilizer is a security device designed to prevent unauthorized access and theft of vehicles. It is an electronic system that works in conjunction with the vehicle’s ignition system. The immobilizer requires a specific electronic key or fob, often equipped with a unique code or transponder, to be present in the vicinity of the car in order for the engine to start. 

Without the correct key or fob, the immobilizer prevents the ignition system from engaging, effectively immobilizing the vehicle and thwarting attempts at hotwiring or unauthorized use. This technology enhances the overall security of modern vehicles, acting as a deterrent to potential thieves and contributing to the protection of valuable assets.