“Ever wish you had a tool that could prove your suspicions were valid?” Bluewater Security Professionals asks on its Web site (bluewatersecurityprofessionals.com). "Next time you sense suspicious activity with your vehicle, make sure (the $435 PTS Tracking System) goes along for the ride. The site includes “hints” on where to put the GPS antenna—mostly in places where it wouldn't be seen. But forewarned is forearmed: Here are some of the spots where a GPS unit is likely to be stashed.