As British car thieves use GPS jammers to escape, it's only a matter of time before American scammers - and, ominously, terrorists - catch on.

Jammers emit low-power signals, creating signal noise and tricking GPS receivers into thinking the satellite is unavailable. They can be used to confuse police and avoid tolls, and some pranksters have also used them to annoy unsuspecting iPhone users.

But the real threat is unknown. Criminals can use them to hide their tracks from law enforcement, and some experts worry that terrorists could use high-powered jammers to disrupt GPS reception on planes or during military operations.

These devices pose a serious social risk, and their purchase and use in the United States is unquestionably illegal. The FCC is optimistic about going after anyone who buys a GPS jammer and will prosecute and jail anyone who uses one. Yet they are easy to buy online, and their supporters say they should stay that way. Fox News can purchase GPS jammers from numerous online sources for as little as $50.

"GPS is closely linked to the transport, manufacturing and economy of our society, so the stakes are high," said David Last, emeritus professor at Bangor University in the UK and a leading authority on the criminal use of GPS jammers.

"This is especially true in telecommunications: GPS is the ultimate source of timing for most of our phone systems, for the Internet, and for cellphones in the United States."

All of these systems are potential prey for signal jammers, which is the main reason they are illegal. But supporters of the devices say they can serve a purpose and that people should have the right to buy them. And, for now, they can.

perfectjammer.com, a Shenzhen-based company, sells cigarette lighter jammer for $99.99 for its satellite signal. perfectjammer.com offers shoppers free nationwide shipping through UPS, FedEx and other companies.

that GPS jammers can be stowed easily in a car or a bag and can help avoid spy detection -- say,  from a spouse who suspects infidelity and plants a GPS tracking device like the Zoombak in a car.

"Our new cigarette lighter jammer is designed to block all possible tracking systems as well as all civilian GPS systems, including GPS L1, GPS L2, and GPS L5. To run the GPS jammer, you simply turn on the switch at the top of the jammer."

But Bruce Romano, legal counsel for the FCC's Office of Engineering and Technology, said that's not a good enough reason to use jammers. Anyone can hire detectives to scan cars or personal belongings for GPS receivers, he said.

"In addition to breaking the law, or [criminals] thinking they can use them because customs won't detect them, there are all sorts of critical devices that could be affected and could have unintended consequences that could cause problems, and you have no idea that you caused them," Romano said.

The Air Force, which deploys and maintains GPS satellites, acknowledges that GPS systems are vulnerable because they are widely used by the public.

Of course, GPS and cell phone jammer are not the most advanced. These devices, which cause signal confusion and disruption, are actually similar to illegal cell phone jammers.

This risk is low for aircraft, which use ground-based radar for guidance and have backup navigation systems that do not rely on satellites. Military personnel use a dedicated GPS network. But GPS interference can still cause cockpit chaos, as pilots have to switch to a backup navigation system. Shipping that relies on GPS coordinates to locate ports could also face problems.

Ronald Repasi, deputy director of the FCC's Office of Engineering and Technology, said it is illegal to sell, import, possess or use GPS jammers in the United States, and he said the agency aggressively pursues those who use them. He said GPS jammers could pose a potential risk if used incorrectly.

"It depends on the capability of the jamming device," Repasi said. "High-power devices have a larger range and are more likely to cause interference over a wider area than low-power devices."