A smart entry system is known in the art, for example as disclosed in JP 2001-115705 A. In this system, an identification code (ID) transmitted by a portable device is compared with a specific ID assigned to a vehicle when a user having the portable device for a smart entry approaches the vehicle. A door of the vehicle is unlocked if the ID of the portable device corresponds to the specific ID.
The smart entry system has a push-start operation, so that an engine start is attained by only pushing a push-start switch provided in the vehicle if the ID of the portable device corresponds to the specific ID.
The portable device cannot transmit the ID when it is broken or its battery runs down. In this case, the ID is sent to an Electronic Control Unit (ECU) controlling the smart entry system by a transponder operation of an immobilizer, in which the ID is sent by energizing a coil in a slot, so that the ID is compared with the specific ID, when the portable device is inserted into a slot and the push-start switch is pushed. In this way, a backup comparison can be executed when the portable device is broken or its battery runs down.
However, the slot is provided at the vehicle only for the backup comparison, although the backup comparison is not made very often.