They also make an audible pinging sound soon after eight hrs far from its operator. While this is a great privateness and basic safety function for the general public, this can wreck the discreteness of the tracker. Some (however none analyzed here) will incorporate VHF monitoring together with GSM positioning https://www.trackerfit.co.uk/blog/stolen-car-recovery-why-24-7-monitored-trackers-make-a-difference/