Perman Electromagnetic Auto Car Safety Parking Reversing Reverse Backup Radar Sensor Size: Main Module: 5.8 x 3.4 x 1.8 cm Alarm Horn: Approx 4.8 x 3 x 1.6 cm. Wires to \"Reverse Lamp\" (12 Volts DC) Peel and Stick foil tape sensor for vehicles with non-metal bumper. Electromagnetic field changes as object get closer to the bumper. Electromagnetic sensor. Automatically beeps to alert near-by objects. Detects people, vehicles, small & high kerbs, garage doors, pillars, posts, walls, fences, barriers, skips, etc. Improves parking safety. Minimize bumper damage. Indicates object distance with different beeping frequencies. Easy and concealed \"inside bumper\" installation.