US Patent 7224261 Vehicle security system

When transmitting an instruction for activating an immobilizer function to a vehicle, a base station also transmits a given password for releasing the immobilizer function. When receiving the instruction and the given password, an immobilizer ECU outputs an instruction for prohibiting an engine from starting. Prohibition of engine start is released only when the given password is inputted on a display. Therefore, a regular user alone, who knows the given password, can start the engine.