If you suspect your vehicle is being tracked, this is a genuine cause for concern. Especially if you never consented to have your movements tracked. Vehicle tracking is a means by which third parties can monitor your movements, the speeds at which you drive and even the intensity with which you apply the brakes. If you believe you're being tracked, you are entitled to investigate further.
Why are you being tracked?
The reasons for tracking you are numerous. Some are legit, some less so. For example, your insurance company may track you using telematics. This is legitimate. You have to give them permission to do this, and in return, you may benefit from cheaper insurance premiums. Your employer may also legitimately track your vehicle, but you must give them permission to do so. Most often, this is done when you sign your employment contract.
Is this legal?
The legality of vehicle tracking depends entirely on whether the subjects reasonable expectation of privacy has been breached. In most circumstances, you'd expect a high degree of privacy in your vehicle. But if you sign an employment contract or insurance agreement that says you consent to vehicle tracking, you effectively waive your expectation of privacy. The payoff is you get cheaper insurance, or you get that driving job you applied for. It gets legally murky when permission isn't granted. Boiled right down; it's illegal to track someones vehicle without their permission.
However, if tracking forms part of a legitimate investigation - for example, you're a concerned parent worried that your child had been roped into criminality - the public interest factor may mitigate the breach of privacy. So, if you think you're being tracked and you're damn sure you didn't consent, you need to put a stop to this.
How to know if you're being tracked
The first suspicion you're likely to have is when people appear to know more about your movements than they should. This could be a competing business person who seems to be at the same places as you with suspicious frequency. It could be the former partner who asks 'what were you doing in Manchester last Tuesday night?' It could just be the presence of the same vehicle in your mirror too often to be a coincidence. Unless you make a habit of checking your vehicle for trackers, intelligence will be your first tip-off. You may also be suspicious of any undue attention given to your vehicle.
Has it recently been towed away or impounded? Has a friend, business partner or family member taken it to a garage for repairs that you were not initially aware of? Has anyone else who uses the car had anyone come out to work on it? A mobile locksmith, for example? If anyone other than yourself has had access to the car, ask yourself why. Once your suspicions are raised, you need to check your vehicle.
Start with the wheel arches. These are the go-to location for magnetic car trackers as they are easy-to-access but difficult to spot. Following that, check all the parts of the car where a non-mechanic could quickly gain access. The spare tyre, the glove box, the little nook in the boot where your spanners go. Look out for carpet that has been disturbed or facias that appear to have been tampered with.
How to stop yourself from being tracked
The best and most obvious way of doing this is to remove the tracker physically. You may need the assistance of a mechanic to help you tear down the car and identify the device. This can be expensive. You may also wish to consider selling the car and replacing it. This sounds drastic, but not only will it stop you from being tracked, but it also has the added benefit of feeding bad information back to whoever may have been tracking you.
Other means of counter-surveillance
If you're sure you're being tracked, you can try the Breaking Bad method of counter-surveillance. Now you know you've got a tail, use it to your advantage. Make confusing or aimless journeys, establish patterns that mean nothing, or ensure you make commercially or privately sensitive journeys by other means. In short, if someone is tracking you, you are well within your rights to mess with them.