The Emergency Management and Response—Information Sharing and Analysis Center (EMR-ISAC) recently ran an informational piece on "Jamming Devices", that it described as:
"...illegal radio frequency transmitters that are designed to block, jam, or otherwise interfere with authorized radio communications. Jamming technology generally does not discriminate between desirable and undesirable communications. A “jammer” can block all radio communications on any device that operates on radio frequencies within its range."
Primarily hawked as a way to create cell phone "quiet zones" in restaurants, schools, theaters, and other similar public places, these systems are illegal to market, sell or use in the United States because of the degradation they can cause to public safety communications outside the intended zone of jamming. Nonetheless, the Federal Communications Commission (FCC) has become very concerned about a signiciant increase in the number of websites selling these devices. Recently, GPS jamming devices have been added to the mix.
Similar in concept to cell phone jammers, GPS jamming devices are designed to keep your boss, family, police, or the company whose truck you just stole, in the dark about "where you are". For obvious reasons, they are also illegal to market, sell or use in the United States. However, despite a crackdown by the FCC that started earlier this year, a brief check of websites finds them available for anywhere between $120 and $400.
Here are some links if you would like to know more about the issue of GPS jamming: