Tracker is effective, but not always. The night my car got jacked the weather prevented the police helicopter (it was raining ??) so they could not pursue despite me notifying Tracker immediately. They had to rely on the in car units to locate the car, which as it happened had been abondoned half a mile down the road.
Another point on Tracker. Do you really want a car back after it has been stolen? I somethimes think I'd have been happier never to see my again. The hassle getting it back, and then the way it doesn't feel the same....