I use one from these guys.

I'm not really using it to it's potential ( it has various inputs and outputs to do stuff if wanted ), but it does what I need, and well it seems to work.

https://www.rewiresecurity.co.uk/veh...acking-devices

I'm sure one of the most important items for any tracker other than the hardware itself, is how you actually view or use the data etc and this one seems pretty good.