The present invention relates to a vehicle antitheft system for deterrence against vehicle theft. 
One conventional antitheft system as disclosed in a Japanese Patent Provisional (Kokai) Publication No.  64(1989)-56253 employs an ignition key having therein a transponder for transmitting an ID signal.  A vehicle immobilizing system checks the ID signal of the transponder each time the engine is started, and generates a permission signal to permit the engine operation if the received ID is verified, and an inhibition signal to immobilize the vehicle by interrupting the engine operation if it is not. 
A keyless entry system on the other hand is designed to enable a driver to enter the vehicle without inserting a key into a keyhole, but simply by pressing a button of the key.  The keyless entry system receives an ID signal transmitted from a keyless remote controller formed in the key, and performs door locking or unlocking operations. 
In conventional systems, however, a failure of the transponder makes it difficult to continue the engine operation.