Teen tracking with GPS. Found this interesting site on the web called Teen arrive Alive (TAA). The point is to use their service you get a cell phone for the kid, get a Nextel cell account, and the GPS location of you child can be downloaded at any time from the internet.
The lower cost option is a decal you get for your car and the cell phone. Instead of GPS the decal has a phone number concerned drivers can call and inform you of how your teen is driving (like "hows my driving? Call...").