Abstract: In a crew member detecting device, an acoustic wave generator element mounted on a vehicle body generates a standing wave between the acoustic wave generator element and a bucket seat, and an acoustic wave receiver element is provided in the region of the standing wave, to detect the presence of a person on the bucket seat from variations in the output of the acoustic wave receiver element which are due to the movement of the person on the bucket seat.

Abstract: A passenger protecting device of a motor vehicle includes an acceleration sensor which issues an acceleration signal representative of the degree of a vehicle collision; a signal processing circuit which, by processing the acceleration signal, issues an ignition trigger signal when judging that the vehicle collision is critical; a DC power source for charging a plurality of back-up capacitors; a plurality of squibs each having first and second terminals, the first terminals of the squibs being connected to a common terminal and the second terminals of the squibs being connected to the back-up capacitors through respective connection lines; a first switch circuit having one terminal connected to the common terminal and the other terminal grounded; and a plurality of second switch circuits, each being disposed in each of the respective connection lines, each second switch circuit being turned ON when receiving the ignition trigger signal from the signal processing circuit.