The Audi Parking System (APS) makes parking easier. An intermittent warning tone indicates how far the car is from an obstacle. As the distance decreases, the warning tones become faster. It first sounds when the car is just over 5 feet from the obstacle and sounds continuously when only 8 inches remain. The APS uses ultrasonic sensors that can be installed at the rear as well as the front of the car, depending on the model. It can be switched off via a button on the instrument panel for special situations such as stop-and-go traffic. When the reverse gear is selected, APS is switched on automatically.