GE SmartHome Parking Alert Ultrasonic Sensor Ultrasonic sensor parking alert. Sensor detects distance of car from wall. Yellow & red indicator lights tell when to slow down or stop. Features ultrasonic, range-finding technology. Automatic Low Battery Indicator. Choose from 3 stop zones: 1, 2, or 3 feet. Required 4 "AA" batteries - not included. Easy installation. Comes with instructions.