Abstract: A diaphragm-type transducer assembly is mounted on the rear of an automobile to transmit ultrasound into left- and right-hand target regions near the automobile. Spoilers are mounted adjacent to the transducer diaphragms to disrupt the air flow around them and prevent negative pressure that could adversely affect the operation of the transducer. The circuitry for driving the transducers includes relays in the signal-lamp circuit to detect when the turn signal is turned on, and it only transmits ultrasound pulses in response to signal-lamp actuation. The system initially "listens" for objects outside the target region in order to test the circuitry, but it subsequently responds only to objects within the target region.