First Alert SFA275 Parking Alert Sensor Easily Mounts on a Wall, Workbench, or Shelf in Your Garage Features Ultrasonic, Range Finding Technology, with 3 Different Light Indicators and Alert Sound Green Indicator Lights When Within 16 to the Sensor (Slow Down), Yellow Lights When Within 5 (Proceed With Caution), Red Indicator Lights Within 1.5 of the Sensor (Stop) On/Off Switch AC Adaptable (AC Adapter Included), Power: 1 x 9V Battery (Not Included)