For anyone who's ever dreamed of having the power to silence obnoxious cell-phone conversations, a cell-phone jammer sounds heaven-sent. Unfortunately, these devices are illegal in the United States. The Federal Communications Commission says making, selling, importing or using a cell-phone jammer is punishable by a fine of up to $11,000 and imprisonment for up to a year.

Mechanism of cell phone jammer

Cell phones are essentially two-way radios. They send and receive signals on bands of the electromagnetic spectrum reserved for their use. (In North America, those frequencies are clustered around 800 and 1,900 megahertz.) Cell phone jammers work by sending out an extremely powerful but short-range signal on those same frequencies. The signal overwhelms cell phones in the immediate area, making it impossible for them to connect with cell towers. To a cell phone user in an area where a jammer is operating, it appears as if there is no available signal at all. Modern handheld jammers--not much larger than a cell phone themselves--have a range of about 30 feet. Bigger units can affect entire buildings.

Ban about cell phone jammer

The federal government bans the possession or use of cell-phone jammers by anyone except law enforcement or other authorized agencies. It's also illegal to sell jammers to unauthorized persons or to import them for non-approved use. A similar ban is in place in the European Union. Even so, according to the technology review website Method Shop, people can and do buy jammers from overseas sellers and have them shipped into the United States. Jammers are legal in many countries in Asia; in 2007, the New York Times reported on a merchant in India who regularly fills orders from the United States.

Safety of mobile phone jammer

There are two main rationales behind the ban on cell-phone jammers. The first centers on safety. Sure, turning on a cell-phone jammer might guarantee that no one will carry on an obnoxious conversation--but it also guarantees that no one will be able to use a cell phone to call 911 in an emergency. Jammers would also interfere with communications among the emergency responders themselves. And cell-phone jammers would also be of great use to criminals. Bank robbers, for example, could use a jammer to keep witnesses from calling police until they had fled.

Theft of cell phone jammer

The second argument against jamming is that it may amount to property theft. The law considers the airwaves public property, with the federal government serving as the administrator of that property. As outlined in Slate magazine, this anti-jamming argument holds that cell phone service providers have paid billions of dollars for licenses to operate on the affected frequencies. Jamming the use of those frequencies deprives the providers of the right to use property that they have paid for.

Official Use

Law enforcement agencies use cell-phone jammers to cut off communications in certain situations, such as hostage-taking incidents. When a criminal is holed up with hostages, police want to be able to control communication with that person. They can switch off all but one telephone land line going into a building, then use a jammer to make sure the hostage-taker can't use a cell phone to contact accomplices or the news media. Jammers can also be used to establish a security perimeter. Terrorists commonly use cell-phone signals to detonate bombs remotely. Convoys in Iraq have used jammers as a protection measure, and, according to CNN, the presidential motorcade includes a vehicle equipped with a jammer.