Just because of my own bad experience I'd not recommend the "Tracker" company (as above) - I bought exact same model and the company showed such incompetence at several stages of the process that I realized the chance of them being able to find my car was low and there were better models coming on the market. So I ended my Tracker subscription and signed up with iMob with whom I still have a subscription 6 or 7 years later (although the firm changed hands about 3 years ago). They have a call center that manages alerts and the TT4 model I have does accident detection (the ice-plate at Porsche Experience Centre Silverstone set that off) and also a panic alarm in addition to the usual. It also lets me talk to it direct - so I can text it to find out where it is (for example if I've left it at OPC for an MOT and I'm wondering if its out on a "test drive"). Oh and the call centre can immobilize the car if the police ask them to.
But TBH the market's a real mess now because you can get all these features for a few pence on ebay (except the call center). If you need it for insurance fine, but you do end up paying quite a lot for the call centre feature. But if you want that I'd recommend the iMob TT4.
