BOB GARFIELD: So being tracked by GPS is creepy. It turns out that trying to evade GPS tracking by disrupting it is downright dangerous. So says News Scientist Magazine’s David Hambling, who recently wrote that just a few bucks spent on a dashboard-mounted device can jam GPS signals, and that can have potentially catastrophic consequences.

DAVID HAMBLING: For about 20 dollars you can buy a unit that will jam every GPS system within range. Because the GPS satellites are only broadcasting at a power of about 10 watts and they're 12,000 miles away, anything that’s broadcasting, say, 1 watt or something like that, the kind of output of a mobile phone, that will completely overwhelm the signal from a satellite a long distance away.

BOB GARFIELD: Now, if we were only using GPS to find the nearest Starbucks, that would be one set of problems. But we rely on GPS to do many, many things that most people probably aren't even aware of. Can you give me a short list?

DAVID HAMBLING: It’s described as an invisible utility, and that’s about right. Because it’s a means of providing extremely accurate time signals very cheaply, 'cause you get a, a 10,000-dollar atomic clock, effectively, for 10 dollars, it’s used in a lot of services that require very accurate timing. Cellphones need an accurate time signal to synchronize their signals. Power utility companies use it to synchronize the output of alternating currents so they can plug into each other. Financial services use it for sending encrypted communications.

BOB GARFIELD: Give me some examples of how easily GPS signals have been jammed and the consequences of those incidents.

DAVID HAMBLING: Well, there was a, a very unfortunate incident last year at Newark Airport. They'd just installed a new landing approach system for use in bad weather which would allow pilots to land when they couldn't see, and they found that this was shutting itself down twice a day. And the reason turned out to be because it relies on GPS, and there was some guy driving past in a truck twice a day with a GPS jammer. It might have been to avoid road tolls, 'cause there are some toll roads there that use a GPS-based system to calculate where the vehicle is and how many miles it’s done on the toll road.

BOB GARFIELD: Oh so, he’s on the New Jersey Turnpike and [LAUGHS] this is his way to exit the turnpike without having to pony up. If GPS can be so easily, inexpensively defeated for the most mundane of reasons and if we so depend on it, what’s the solution?

DAVID HAMBLING: The experts I talked to all agreed on the same solution. It’s a thing called LORAN, which is an older system than GPS but it’s like a land-based version, rather the satellite-based version. So it only has a range of about a thousand miles or so, but with a fairly modest system you can cover the continental U.S. Because it’s land-based it’s a, a much more powerful transmitter and it’s broadcasting on a longer wavelength. And that makes it pretty much impossible to jam. And it’s very easy to build system that will receive GPS from satellites as well as LORAN, so if GPS is jammed it simply switches to the alternative.

BOB GARFIELD: But that would require building many terrestrial LORAN installations, right?

DAVID HAMBLING: The system is already there. It was built in the '50s and was used for many years by aviation and maritime. But unfortunately, in the U.S. this system’s now being dismantled. I believe there was a fairly small saving involved, about 30 million dollars, and there’s a lot of experts in the field who say it would make a lot of sense to get that back up and running before something disastrous happens.

BOB GARFIELD: Tell me what disastrous could happen.

DAVID HAMBLING: We had a, a small taste of it in San Diego in 2007 when a Navy exercise accidentally jammed GPS in the area. Not only were navigation systems lost in the harbor, in the airport, but also a lot of cellphones went out of action, cash machines stopped working. The paging system at one of the hospitals, used for summoning doctors, stopped working. And those are only the ones we know about.

BOB GARFIELD: If LORAN has been so dismantled as to make it impracticable to set it back up, where does that leave us?

DAVID HAMBLING: It can be set back up if someone wants to spend some money on it. The cost of setting it up against would be a fraction of the cost of one GPS satellite, and there’s a total of 31 of them in orbit at the moment. So just for a, a very small extra expenditure it could make sure that that kind of catastrophe could be avoided.

BOB GARFIELD: David, thank you very much.

DAVID HAMBLING: My pleasure.

BOB GARFIELD: David Hambling writes for New Scientist Magazine.