Jamming the signals on which we depend

A few weeks ago I rented a car for a few days. It had a GPS navigation system, and although I didn't need it in the areas where I was driving, I began to use it out of curiosity, to get accustomed to its operation. It didn't take long before I began to notice periods - usually on an interstate highway - when the system lost the GPS signal altogether. Observation led to the conclusion that they usually coincided with the passage of a large commercial truck or van.

I asked a friend in the local law enforcement community about this phenomenon. He ascribed the problem to GPS jammers. He said that many companies use GPS systems to track their vehicles' location and movements. However, corporate drivers frequently object to this, and so use GPS jammers to disable such systems. Furthermore, law enforcement agencies have been known to attach GPS tracking devices to vehicles, in order to follow them and/or build up a record of their drivers' movements (although this will be more restricted in future, in the light of a recent Supreme Court decision). Criminals use GPS jamming devices to frustrate such efforts. He believed the 'dead spots' in GPS navigation that I'd encountered were caused by a vehicle carrying a GPS jammer, traveling in close proximity to me for a few miles.

Intrigued, I did a bit more research on the topic. Truckers and other drivers using GPS jammers have been known to interfere with aircraft and airport navigation systems. Military jamming tests have disrupted not only GPS signals, but also cellphone, pager and other important commercial systems. In the UK (and, presumably, in this country as well) organized crime routinely employs GPS jammers when stealing or hijacking vehicles, to frustrate any tracking hardware or software that may be hidden on board. Prisons are faced with huge security risks in the proliferation of cellphones among inmates, who use them to communicate with family members and gang associates, arrange drug deals, plan escapes, and even organize 'hits' on criminal rivals, or potential witnesses against them. There have been proposals for many years to restrict (i.e. jam) or control cellphone transmissions in and around prisons, but so far this has been resisted by cellphone service providers and the FCC (the latter having also increased enforcement against illegal jamming of signals). Schools, too, want to prevent students using cellphones during class, and at least one school has successfully tested a cellphone jamming device.

I was surprised to see that, despite their sale being (at least technically) illegal, jamming devices are freely available online. One company even advertises quite blatantly that you should buy one of their jammers to ensure a cellphone-free evening at the movie theater! Clearly, the law hasn't kept up with the problem - and, given that one can order such products from overseas suppliers, it probably never will succeed in effectively controlling them.

I'd be interested to hear whether readers have encountered problems with jammed GPS or cellphone signals in their daily lives. If you have, please let us know about it in Comments. Also, if you know of ways to get around the problem, please tell us about them. We might all learn something.

Peter