With all doors locked, the driver and front passenger door oscillators form a smart key detection area outside of the vehicle by emitting smart key detection signals on a regular basis. Accordingly, the smart ECU will be able to check the ID code of a smart key in the detection areas.

With all doors locked, if a user presses the back door opener switch, the back door oscillator starts to form a smart key detection area outside of the vehicle by emitting signals. Accordingly, the smart ECU will be able to check the ID code of a smart key in the detection area.

With all doors closed, if a user presses the lock switch on the outside door handle, the smart ECU will cause all the oscillators to emit signals in order to form smart key detection areas outside of the vehicle. Accordingly, the smart ECU determines that the smart key has been taken out of the vehicle.

If a user operates the power switch while the smart key is in the user's possession, the smart ECU outputs a request signal to cause the room oscillator to emit signals in order to form a smart key detection area in the vehicle interior. Accordingly, the smart ECU will be able to check the ID code of the smart key, even if the smart key is not inserted in the key slot.

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