My cousin has a tracker in his Astra VXR (standard fit I believe?) and it led to the swift recovery of it with the guys that stole it stood next to it!
They had also broken into the house, walked through picking up a laptop on the way.... Then decided to leave through the window after they realised a hideously overgrown bulldog/bull terrier was on the other side of the lounge door. My cousin an his missus thought he was just being annoying, ah well, stopped them going upstairs.
He's now got what's known as 'dealer doors' nigh on impossible to break down or into. I'm sure a google would bring something up.