Yeah,I know I mentioned these before but now they even text you if your vehicle leaves a safe zone and you can set it to record it's location every 5 minutes for an hour automatically! You can also check your vehicle from your phone. It's pretty cool if you ask me! The service is $10/month tho' and the unit is around $200 at Best Buy or Petsmart. BTW it uses both GPS and cellular signals.
http://www.zoombak.com/