Back 7 years ago when I was just starting on my first job I had the chance to work as a software developer for a company witch build the hardware and software for a product witch monitor a fleet of trucks with the help of GPS and the GSM networks. At that time the device needed for that was the size of a laptop, need a truck service to be installed and I can tell you that was not cheap.
This morning I had stumbled on an Android app named CarLock witch with a help of a small device do almost the same as what the system I was talking above did.
It track the position of a car, and you can see it in real time on a map from your phone or tablet, you can get notification if the car is moved from the location where you left it and you are notified if the system lost GPS or GSM signal or the device is removed from the car (it is a strong chance that someone steals your car and try to remove any traces).
If you ask yourself at this point how a simple phone app do that, remember what I said at first. You need a device that is connected at the car computer. This device can be purchased from the CarLock home site carlock.co for the price of 99 Euro and you get bonus one month subscription in that money.