A vehicle occupant protection system includes a buckle switch that senses the condition of wearing a seatbelt, a first detection circuit including a first switch that is in the open position when the seatbelt is in use and is in the closed position when the seatbelt is not in use, and a second detection circuit including a second switch that is in the closed position when the seatbelt is in use and in the open position when not in use. An ECU supplies power to the first or second detection circuit whose switch is in the open position. The ECU also controls a motor in response to a detection signal outputted from the first or second detection circuit that is supplied with power. The sleep mode of the ECU is canceled when the detection signal outputted from the first or second detection circuit that is supplied with power changes.