How Do Parking Sensors Work?

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While the difficulties of parallel or reverse parking are not quite yet a thing of the past, advancements in technology have helped ease and, in some cases, eliminate the process. But what are parking sensors and how do they work?

What are parking sensors?

Parking sensors, also known as proximity sensors, are devices that are located on the bumpers of a vehicle in order to assist the driver when parking. They measure proximity to an approaching object, either in-front or behind, and alert the driver if they get too close. The sensors usually emit a beeping tone that gets faster and more frequent as the object approaches.

There are currently two types of parking sensor on the market, ultrasonic and electromagnetic, and while they both do the same thing, they do so in different ways.

How do they work?

Ultrasonic Sensors

parking sensors front

Ultrasonic sensors work while stationary or while moving and use sound waves to detect objects in-front of the sensor. By pulsating sound in a high-frequency that reflects off near-by objects, a receiver can catch the reflected waves and calculate the distance to the detected objects.

Ultrasonic sensors either emit a sound to alert the driver or translate to a pictograph that uses colour to represent the vehicle and objects. However, there are disadvantages and ultrasonic sensors may not be able to detect objects that are:

  • Too thin to reflect sound e.g. posts and bollards
  • Too low to be detected e.g. the curb
  • Too flat, as they won’t reflect sound back as well
  • To the side, as ultrasonic sensors only pick up objects directly in-front

Moreover, ultrasonic sensors are affected by interference which means anything obscuring the sensor e.g. a bike rack, affects how the sensor builds its model of the surroundings.

Electromagnetic sensors

parking sensors rear

Unlike ultrasonic sensors that can only detect objects in-front, electromagnetic sensors can detect objects surrounding the entire vehicle. These sensors use frequencies to create an electromagnetic field which can detect anything that enters it. As a result, this means that electromagnetic sensors don’t work when stationary, unless the objects themselves are moving e.g. pedestrians or other cars.

While they may not work as well while stationary, electromagnetic sensors don’t suffer the same interference problems as ultrasonic sensors. They are also more sensitive which allows them to pick up objects that ultrasonic sensors can’t. However, while they don’t have any pressing disadvantages, they are typically more expensive than their ultrasonic counterparts and may not be suitable when shopping on a budget.


Even though parking sensors are great assistance tools that significantly ease the task of parking, they can be considered lacking to some. As such, some manufacturers offer alternative assistance tools that can work in isolation or in conjunction with parking sensors to greater simplify and improve the parking experience.

Reversing Cameras

I3 reverse parking camera

Rear facing or reversing cameras give you a live feed direct to your infotainment display that allows you to see what’s behind you as you attempt to park. Rather than relying on sensors and guessing the unknown, reversing cameras clearly show your surroundings. This allows you to determine whether or not the curb is too high for example, or if you can swing around that wall on the left-hand side.

Unlike sensors, there are no warnings with reversing cameras and while they may provide the driver with more information, there is no alert should the driver have misread that information. As such, most manufacturers pair reversing cameras with parking sensors so that you have both visual and audial cues while parking.

360 Degree cameras

360 degree camera systems are a step-up from reversing cameras and are at the higher end of the market. They use numerous cameras spread around the vehicle to produce a bird’s eye-view representation, which helps you to visually determine how close you are to objects on the sides as well as the front and rear.

Some 360 degree camera systems, like the one in Volvo’s XC60, allow you to cycle through all cameras to see the feed from just that camera. For example, choosing one of the door mirrors can help you judge whether or not you are too close to the kerb or if you are within the lines of a parking bay.

Parallel Parking

Park assist systems

While park assist systems technically still rely on sensors, they do so with minimal manual input and allow drivers to effortlessly parallel park in five easy steps.

  1. The car moves forward beside the car in the space in front and signals the driver to stop.
  2. The driver put the car into reverse and begins moving backward.
  3. The car takes control the of the power steering system and manoeuvres itself perfectly into the space.
  4. The car backs into the space and signals the driver to stop and put the car into drive.
  5. The car drives forward while adjusting the wheels and straightening out.

More and more cars now showcase self-parking systems in their specifications and the majority of manufacturers now offer park assist functionality as an additional extra or on a more expensive trim. 

Now that you know how parking sensors work, the differences between ultrasonic and electromagnetic cameras and the other alternatives on the market, why not include parking sensors or park-assist as part of the specification for your personal or business dream lease car?

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