How Do Parking Sensors Work ?

Thinking back to preparing for my driving test 30 years ago, the one part that kept me awake at night was parallel parking. Fast forward to the present day and not much has changed, except now I know there isn’t much chance of me reversing into the car behind me. The reason for this is the widespread use of vehicle parking sensors which are, in my opinion, the greatest vehicle safety invention since the seatbelt. Lets dig a little deeper and ask ourselves two key questions. What are Parking Sensors? & How Do Parking Sensors Work ?

What Are Parking Sensors ?

Parking sensors, also known as proximity sensors, are devices mounted and recessed into a vehicle’s bumpers that aid the driver during parking. We should point out that Parking Sensors are not to be used as a substitute for your eyes or reversing mirrors. They are designed to help you with your reversing and parking manoeuvres.

How Do Parking Sensors Work ?

Parking Sensors calculate the distance between the driver and an approaching object, either in front of or behind them, and trigger an alarm if the driver gets too close. As the object approaches, the beeping alarm gets quicker and more frequent. This will happen in stages, so the beeps will start slowly at about 1.5m and become quicker as you get closer to the obstacle. The tone becomes solid and unbroken at about 30cm. These distances vary between manufacturers, but the concept remains the same.

Flush Mount Parking Sensors Working
Flush Mount Parking Sensors Working

Different Types Of Parking Sensor Technology.

Most aftermarket backup sensors that you will purchase in the UK are made using one of two types of technology.

1. Ultrasonic Parking Sensors.

Also known as Ultrasonic Parking Assist, they work by bouncing sound waves off the objects in front of them. They work while stationary or moving, and calculate the distance to the object based on the time it takes to detect the reflected sound wave. The distance is represented via an audio beep or visually via a numerical distance on an LED display.

Problems With Ultrasonic Sensors.

In the years I have spent marketing and selling Ultrasonic Parking Sensors, only two real issues have ever been reported back to me by our customers. The first is blind spots. Ultrasonic Sensors need to be placed no further apart than 30cm. If they cannot be fitted within this range, the detection catchment area will have a small blind spot. While this will not be a problem 99 times out of 100, if you are reversing directly onto something narrow (like a lamp post or bollard), the sensors might not detect it.

Parking Sensors Without Blindspots


Ultrasonic Backup Sensors With Blindspots

The second issue is rain. Yes, that is correct precipitation. As we stated earlier, Ultrasonic Sensors bounce sound waves off the objects in front of them. If the rain is heavy enough, the sensors will read this as an object and trigger false alerts. Again, this is an issue that will generally not cause a problem. But it can be frustrating at times.

2. Electromagnetic Parking Sensors.

Unlike ultrasonic sensors, which can only detect objects in front of the sensors, electromagnetic sensors can detect objects all around it. It does this by creating an electromagnetic field which, when breached, triggers an alert. As a result, unless the objects themselves are moving, in relation to the electromagnetic sensors, such as pedestrians or other cars, you will not get an alert.

The obvious benefit to this is that they will work fine if you have a towbar or bike rack on your vehicle, as they will not be detected as an obstacle. Also, they are fitted behind the bumper so there is nothing on show and they do not void the warranty of your vehicle.

In terms of performance, personally I am torn on this one. When we sold electromagnetic sensors, they had a pretty high failure and return rate. However, this was 10 years ago, so things have probably improved. People swear by them online, anyway.

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