Global positioning systems (GPS) may help Americans travel more efficiently, but purchasers should be aware that law enforcement officials are using them as tracking devices. The strategy of monitoring criminal suspects via GPS devices in their cars, cell phones, and boats is often executed without a warrant or court order, raising privacy concerns. On the one hand, prosecutors have used GPS information to convict murderers and rapists, most commonly by discrediting a suspect’s alibi. On the other hand, not requiring a warrant may lead to arbitrary or capricious use of the power on innocent civilians. Renee Hutchins, law professor at the University of Maryland, argues that the current protocol restricts rights granted under the Fourth Amendment of the U.S. Constitution.

"I think that in the last couple of years, people are starting to be aware that if they have these units in their car, people can keep track of you," Hutchins said. "I think it's a growing public awareness. The problem is ... that most people feel like, 'I'm not doing anything wrong, so who cares?' But I think that's the wrong way of looking at it."

Twenty percent of American households possess portable GPS equipment, according to the Consumer Electronics Association. Almost one in ten Americans own vehicles with installed GPS units. The CEA expects portable and in-dash sales of GPS devices to increase from 8.9 million in 2007 to 15 million in 2008. Many attribute this to the significant decrease in cost of mobile GPS units in recent years. Currently, GPS devices can be purchased for as low as $150.