Immobilizer

An immobilizer is an electronic security device built into many modern vehicles to prevent the engine from starting without the correct authentication. The primary goal is to reduce opportunistic theft by disabling the starting system unless the proper key or fob is present.

Most systems include a transponder in the vehicle's key or key fob, an immobilizer or ECU, and interfaces with the engine control unit and ignition/fuel injection circuits. When the ignition switch is operated, the transponder is read by a receiver; if the transmitted code is recognized as valid, the immobilizer releases the engine control unit to allow starting; otherwise the engine cannot be started or will die shortly after starting.

Two main categories exist: passive immobilizers, which require no explicit action beyond carrying a programmed key, and active/improved systems that may require a signal from the fob or a short cryptographic challenge-response. Modern systems often use rolling codes and cryptographic keys, and are integrated with the car’s CAN bus and diagnostic interfaces.

Immobilizers became widespread in the late 1980s and 1990s as car manufacturers sought to curb theft. They are now a standard feature in many regions, sometimes mandatory for new models or insurance requirements. While effective at preventing hot-wiring and similar attacks, immobilizers are not foolproof, and thieves may exploit vulnerabilities or compromised keys.