An immobiliser or immobilizer is an electronic security device fitted to a motor vehicle that prevents the engine from being started unless the correct key (transponder or smart key) is present. The main purpose of the immobiliser is to prevent an unauthorized person from driving off with the car by controlling the starter motor, fuel system, and ignition system. Even if the correct key is used, if the immobiliser does not receive the right code, it will not activate one or more of the aforementioned systems, and the car will not start. This prevents the vehicle from being "hot-wired" after entry has been achieved and thus reduces motor vehicle theft.

While it is required by law for every new car to have an immobiliser, not all systems are equal. Factory-fitted immobilisers are well integrated into the vehicle’s electronics and should work perfectly every time. However, technology is constantly evolving, and some older immobilisers may become vulnerable to hacking. If you are looking to upgrade your immobiliser or don’t have one fitted, it is important to choose a reputable brand and have it installed by a professional.

In summary, a car immobiliser is an anti-theft device that prevents the engine from starting unless the correct key is present, and it is required by law for every new car to have one.