A car is one of the most complicated devices with the most parts that the average person can buy. In modern cars, in addition to the initially not very simple drive chain, there are also several electronic subsystems that serve safety, convenience and comfort.


These are usually invisible, but there are a few small gadgets in the passenger compartment that many people can’t find where to put them. An example of this is the small speaker-like device on the A-pillar, often thought to be a microphone. It mainly occurs in older cars, with a small wire sticking out from under the upholstery, or with other more aesthetic coverings. Some people don’t care about it at all, or think it’s a eavesdropping system as a joke, others think it’s most obvious that it’s some kind of retrofitted speakerphone.

Many cars have it, but many people have no idea why these gadgets are there 2

However, this is not the microphone of the speakerphone, but the ultrasonic motion sensor of the alarm system that monitors the passenger compartment. This is a solution that monitors the interior of the car after locking and activates the alarm at the same time. Sensors usually work on the principle of the Doppler effect, that is, they detect sound waves reflected from a moving object. That way, if something moves in the passenger compartment, or if you are trying to open the radio, the old-fashioned alarm system is already activated.