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The most common form of feedback to the driver in a car with parking sensors is audible "beeps" and/or tones. Generally, the frequency of the beep indicates distance from an obstruction, with the beeps becoming faster the closer the vehicle moves to an object. A continuous tone may be heard when the vehicle is extremely close, often warning a driver to stop immediately to avoid collision.
Some systems use visual aids as well as or instead of audible tones, such as LED or LCD readouts to indicate distance from an object. The direction and distance to the obstacle is indicated by the location and strength of the warning symbols.