I was just reading ERT (for work guv) and saw an Ad. for a GPS tracker type device that is for use to tracks your kids, dog, car etc.
Sounds like a good deal if it powers from your car as you don't need to subscribe, you can simply track online, by SMS, or by calling their call centre

http://www.zoombak.co.uk/

or

http://cgi.ebay.co.uk/New-Zoombak-Ad...1%7C240%3A1318