I accidently left my phone on the table outside the pub the other day (as you do after a few shandys). At ?500 a pop I can only afford to do that so many times!
With this bit of kit I was able to track the phone to the house of the guy who "picked it up" - I think he was a bit surprised when I knocked on his door asking for my phone back
I could tell he'd been messing around with it cause the software will automatically text you if someone changes the SIM (with the new number) - pretty neat in itself