A vehicle immobilizer is a security device designed to prevent unauthorized use of a vehicle. It works by disabling the engine or other critical systems, making it impossible to start the vehicle without the correct key or fob. This technology is commonly integrated into modern vehicles to deter theft. Typically, the immobilizer uses a transponder chip embedded in the key or fob. When the key is inserted into the ignition, the vehicle's engine control unit checks for a matching code. If the code is not recognized, the immobilizer activates, ensuring that the vehicle remains secure.