I think its funny how people think you can actually stop car theft. Unfortunately you can't. If there is one thing I have learnt from horror stories and friends having things stolen its this....
If someone wants to take something enough, they will, regardless of what might be in their way.
Friend had an S1 with wheel tilt sensors, 10foot enclosure, steeringwheel/handbrake movement sensors etc... the most elaborate alarm system I have ever seen. In a locked garage, with 3 cars parked infront of it, a 6foot wall one side of the cars, and two mobile homes the other.
Still, week before christmas last year, woke up, all the cars out on the road, the garage door open and his car gone, Few hours later police found the completely gutted shell on fire in the next village.