The air bag device is provided at the periphery of the lower end portion of the back window provided at the upper portion of the back door, and comprises the air bag cushion to be inflated at the vehicle rear crash, the inflator to supply the high pressure gas to the air bag cushion, and the gas supply pipe to connect the inflator with the air bag cushion. The processing unit stops the output of the pulse signal, when diagnosing a malfunction of the watchdog timer, and diagnoses the malfunction of the watchdog timer based on the first output enable signal output from the latch circuit, after stopping the output of the pulse signal. The system can make a similar alert state change upon receiving an indication of a location-based event such as detection of the user device within a particular building geographic area. The deposited items are passed through the opening and are deposited in a deposit-holding container. The sensor also has a data exchange unit for exchanging data between the transducer, the first communication interface and the second communication interface.