An LED lights up if a body approaches the ultrasonic sensors at a distance of 10 - 80 cm (depending on the size of the body). Use: parking-in assistance for cars in garages, alarm signal for persons or animals staying in a certain area. Operating voltage: 9 - 12 V/DC. The device works according to the same principle as the ultrasonic echo ranging of bats. This kit may be extended to relay operation with our relay board "B197" (not enclosed).