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Why the interest in illegal cell-phone jammers?

Doug Gross, CNN
Jamming an annoying cell phone can also cause others in the area to lose their signals.
Jamming an annoying cell phone can also cause others in the area to lose their signals.
STORY HIGHLIGHTS
  • Philadelphia bus rider spurs interest in cell phone jammers
  • Local TV station interviews man "taking the law into his own hands" to quiet cell talkers
  • Experts say people using the devices could jam police, other communications, too
  • Still, jammers from $40 to more than $1,000 can be found online

(CNN) -- Fancy gadgets that can be used to jam cell phone signals are illegal and potentially dangerous, experts say.

So, why was Google lighting up Monday with people searching for them? You can thank a guy in Philadelphia who got fed up with folks yakking during his daily bus ride and a local news reporter who happens to ride the same bus.

Days after the story broke on Friday, the apparently fresh interest in the devices, which can be had online for anywhere from less than $40 to more than $1,000, is cause for concern among some security experts.

"The general public doesn't realize what they're jamming if they were to start using these things," said Richard Mislan, an assistant professor of computer and information technology at Purdue University who specializes in cyberforensics. "What's not obvious is all the wireless connectivity systems that are in the background and maintaining data communications in our daily lives."

Last week, Philadelphia TV station NBC10 reported on a man who admitted to using a cell-phone jammer during his bus commute to shut down fellow passengers when they were talking loudly.

"I guess I'm taking the law into my own hands, and quite frankly, I'm proud of it," said the man, who the station identified only as "Eric."

He called people using their phones on public buses irritating and rude.

"A lot of people are extremely loud, no sense of, just, privacy or anything," said "Eric," who was first noticed by a writer for the station. "When it becomes a bother, that's when I screw on the antenna and flip the switch."

The story spread. And, apparently, piqued people's interest.

Throughout the weekend, and as recently as Monday afternoon, "cell phone jammer" was one of the top 10 searches on Google Trends, cropping up between searches for Lindsay Lohan's "Saturday Night Live" performance and news about the Super Tuesday primaries.

The legality of the jammers varies from country to country. In the United States, it is generally illegal to sell, own or use one without the government's permission. The devices are offered for sale on a handful of websites.

Mislan, a former communications electronic warfare officer in the U.S. Army, said law enforcement has "very specific worries" about how cell-phone jammers could be used by criminals.

But even someone looking to do no more than hush an annoying neighbor on the bus could do some harm, he said.

For example, in the Philadelphia case, the jammer could have cut off the bus driver's communication with a dispatcher who was trying to communicate emergency or traffic information. And that's not to mention other folks in the area (aside from the offensive loud talkers) who may have missed potentially important phone calls.

"Who is he to play god with our cellphones?" Mislan said.

Jammers work in much the same way online denial-of-service attacks on websites do -- transmitting a signal on the same frequency as mobile phone calls in the area.

"In layman's terms, they basically just interrupt the signals in the area," Mislan said. "They are a louder signal, if you will, than anything else in the area. As a phone tries to connect to a tower, it can't because there's this other noise, if you will, in the way."

Under federal law, illegally using a jammer can result in jail time and fines up to $16,000.

So, if they're illegal and potentially harmful, why is it so easy to find a jammer online?

"It's the Internet. I can buy anything I want, anywhere at any time," Mislan said. "Unfortunately, it's all about the dollar."

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