Reverse sensor, also known as parking sensors, are proximity sensors for your vehicle. This safety device will notify you when there is any unseen obstacle or potential hazard during parking. Usually installed at the rear bumper, reverse sensors work by sending electromagnetic waves that are bounced off the surface of the obstacle. The sensor box will then determine the distance between the rear bumper and the obstacle. The reverse sensor will notify the driver using audible 'beeping' tones. The frequency of the beep tone will indicate the distance between the rear bumper and the obstacle. The frequency of the beep tone will increase as the bumper is nearing the obstacle. Other than audible notification, there is also a visual aid such as LED readouts or gauge to indicate distance between the rear bumper and the obstacle.