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 found in modern cars and is an effective deterrent against theft. Typically, the immobilizer is integrated with the vehicle's ignition system and communicates with a transponder chip in the key. If the key is not recognized, the immobilizer will not allow the engine to start. This feature enhances the overall security of the vehicle, protecting it from potential theft.