I never see the point of a tracker, ex-demos seem to have them on so I have had them in the past but never renewed the maintenance. Thieves don't know you have one - so they are as likely to steal a car with as without. Modern BMWs are I would imagine quite difficult to steal anyway and to be honest once someone has driven my car off at high speed and hacked it about, round the local supermarket car park, I'm not sure I want it back. I also think unless you have the one that detects your car has been moved, by the time you know it is nicked it has probably been found and removed and at the bottom of a lake.
Oops...sorry to resurrect old thread. Clicked through the posts on the latest insurance thread in UK forum