The Federal Communications Commission says illegal devices that block cell phone signals could pose a security risk.

The FCC has seen an increase in the sale of jammers devices that block cell phone calls, text messages, Wi-Fi networks and jammer GPS systems and could be used to wreak havoc in public places.

The small, battery-operated devices can be used to create "dead zones" in a small area (usually about 30 feet) and are used by movie theaters, restaurants and schools to keep people away from their phones. But they also disrupt emergency calls, can disrupt navigation near airports, and have been used near police stations to disrupt radio communications. FCC officials said they have noticed an increase in jammers banned under federal law entering the country. Many cheaper versions are imported from Asia and sell for as little as $95, according to the agency.

The sale, advertising, use or import of jammers is illegal under the Communications Act 1934, which prohibits the blocking of radio communications in public places.

The Federal Communications Commission (FCC) cited eight individuals and companies for ad-jammer ads on Craigslist.

According to the FCC, the jammers were advertised on websites in Orlando, Philadelphia, Austin, Mississippi, Charlotte, North Carolina, Washington, D.C., Cincinnati and Corpus Christi, Texas. Officials said they do not believe the cases are related.

"Merely advertising signal jammers on sites like Craigslist.org violates federal law. Signal jammers are contraband for a reason," FCC Enforcement Director Michele Ellison said in a statement expressed in. “One person’s moment of peace or privacy may well endanger the safety and well-being of others.”

According to the citations, most sellers advertised the jammers for "an undisturbed nap" on the bus, keeping classrooms quiet, or keeping the area "free of nuisances," but there was no suggestion that the device might be used for more nefarious purposes .

"We are increasingly concerned that individual consumers who use jammers appear to be unaware of the potentially serious consequences of using jammers," one of them was quoted as saying. "Instead, these operators mistakenly believe that their illegal activities are for personal convenience or should otherwise be excused.”

But the FCC said at least one seller appeared to know the jammers were contraband.

Keith Grabowski reportedly advertised a "cell phone jammer, Wi-Fi jammer" on Craigslist in Philadelphia for $299.99. He said in the ad, "with few details given due to the nature of the item," that the jammer "is not a toy" and "I just want to get rid of it as quickly as possible."

"The nature of his complaint indicates that Mr. Grabowski was aware of the sensitive and/or illegal nature of the equipment he was selling on Craigslist," his citation reads.

Those facing charges have 15 days to remove the ads from the site and provide the FCC with information about where the jammers were purchased and to whom they were sold. Merely advertising a jammer for sale could result in fines exceeding $98,000.

The FCC has established a jammer reporting hotline to notify the agency of people who may be selling or using jammers.

"We intend to take more aggressive enforcement action against violators," Ellison said. "If we find you selling or operating a jammer, you will pay a high price."