How Does an Automotive Parking Sensor Work?

Written by amanda holden
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How Does an Automotive Parking Sensor Work?
A parking sensor in your car can prevent you from accidentally striking an object while parking. (blue car image by Furan from

Wondrous innovations in car design abound and excite consumers every day, from the novelty of a seat warmer to the practicality of parking sensors. These sensors detect an imminent collision and inform the driver either audibly, visually or both. As simple as parking sensors seem, the particulars of their operation remain fascinating.

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In an ultrasonic parking sensor, a mechanic installs sensors on the front and rear bumpers that emit ultrasonic radio waves. These waves strike objects within the detection range and bounce back, where the sensor measures their travel time. Using this travel time, the sensor will determine whether an object might collide with the vehicle and, if so, activates the warning system. Powerful and difficult to disrupt, ultrasonic waves naturally lend themselves for parking sensors. However, since it uses sound waves, an ultrasonic parking sensor may not detect some small or oddly shaped items that do not easily reflect sound.


Some models use electromagnetic readings to monitor the area near a vehicle's bumpers. Some advertised electromagnetic parking sensors will provide various levels of alarm tones to alert the driver of an approximate distance between an object and his car, offering accuracy of up to 10cm. Because this method uses electromagnetism to detect objects, it has a higher accuracy and can detect objects ultrasonic sound waves may miss. However, sometimes bad weather can affect the electromagnetic system's performance.

Alert System

Humans cannot hear ultrasonic or electromagnetic waves and will need an alert system to notify them of impending danger. An alert box rests within the body of the car, whether factory installed or aftermarket. An ultrasonic parking sensor will signal the alert box wirelessly, while the electromagnetic sensor can be either wired or wireless. Once the alarm sensor inside the box receives the signal, it will notify the driver with an alarm tone, warning light or both.


Ultrasonic parking sensors involve more work and potential damage to a vehicle to install. You must drill holes and leave lasting damage in your vehicle's bumpers to place the sensors properly. An electromagnetic sensor usually attaches an antenna with an adhesive, resulting in no damage to the vehicle's frame, and it disappears from view when installed properly. Some models offer the capability to switch the sensors on and off at will, which can prove useful in slow-moving traffic.

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