The GPS has some limitations because if they pull your vehicle straight into a shipping container, no signal. LoJack doesn't have that problem, but most local cops don't have the expensive lojack equipment.
We've talked about it some, and he has a company in mind. Most of the GPS trackers have you look it up on a computer, you call the cops. so if you're not by a computer... delay. The company he is considering at calls your cell and gets the cops on the other line. You confirm to the cops that indeed, your car/bike is stolen. Then, you hang up and they direct the cops to your vehicle. I think they also have remote disable as an option. If you want the company name, pm me I'll try get it from him.
The one I was looking at would call your phone,email and page you if the car was moved..pretty nice unit. I may have to try one...better then not having anything and have my car stolen...
My part time job has a tracking service that is real nice. All the cement trucks and dump trucks can be tracked via an internet page and the vehicles show up as dots on the "mapquest" like detailed map in real time. The boss is a total cheap ass so it has to be very affordable. Im gonna check it out and post the info.