I used to fit trackers for about 11 years and the only one i would have would be 'Tracker' the problem with all other trackers is they rely on the gsm network to communicate with the operating centre now this bit of kit************************************will block all gsm coverage so the tracker can't send the information it's getting from the gps to the operation centre, where as the 'Tracker' product can communicate through VHF (very high frequency) which you can not block. As mentioned above the police can ONLY track 'Tracker' products using there on board display. VHF can also see through metal (containers) concerte (underground car parks). VHF is not as accurate as gps but with both its a great product. My car has a clifford cat 1 stand alone clifford black jax and a Tracker.