Well, my very first recommendation would be the electronic sweepers. Additionally, you might be familiar with the sweepers under the name of bug detectors.
So, why am I recommending you the electronic sweepers?
To start with their capability of detecting electromagnetic signals. And electromagnetically signals are used by cell phones, radio transmitters, but as well as by GPS tracking devices.
Yet, on the other hand, you should be alerted to the fact that electronic sweepers can only detect GPS trackers that are sending transmissions. So, if you have a hidden GPS tracking device in your vehicle- a passive one, then the sweeper might not seem to be the perfect solution.
Speaking of which, the passive GPS trackers are only sending transmissions when the vehicle is activated.
Nevertheless, if the electronic sweeper detects signal, you will hear it vibrating or buzzing. That way you will be sure that there is definitely a hidden GPS tracker in your vehicle.
What to Do When You Find a Hidden GPS Tracker
So, what can you do once you find out a hidden GPS tracker in your vehicle?
