Yes, so they are basically GPS receivers with a GSM module, constantly broadcasting the location to a central server. They usually have their own battery backup in case the main battery is removed, and have a VHS broadcaster so the vehicle can be found even underground or in a container. For example:

https://www.trackerfit.co.uk/tracker-locate.html

I have a service called "MercedesME" in my car and that provides real-time location of the vehicle at all times by using the built-in GSM modem in the car - but stupidly, in the UK it's not classified as a "tracker" for insurance purposes so having it does not get you an insurance discount.