My brother in law has one on his m3 and it sends him a text every time the car moves off the driveway. It also uses gps, radio signals and another type of signal which police can trace directly and that transmits out of any shipping containers. GPS will stop once its in a shipping container. Also it lets you see where its been driven- it maps it so if you give to a service garage you know if they have been excessively driving it.
There was an attemped car stealing not too far from me and I just got a bit paranoid.