Jammer prevented president's assassination attempt
Cell phone jamming devices were originally developed for law enforcement and the military to cut off communications between criminals and terrorists. The bombs that blew up commuter trains in Spain in March 2004 and the bombs that exploded in Bali in October 2002 and Jakarta in August 2003 all rely on cell phones to set off explosives. According to numerous reports, in December 2003, a cell phone jammer prevented an assassination attempt against Pakistani President Musharraf. When President Bush visited London in November 2004, it was reported that British police were considering using jammers to protect the President's motorcade through London.
In hostage situations, the police can control when and where kidnappers call. Police can block phones during drug operations so suspects cannot communicate outside the area. Cell phone jammers can be used in areas where radio transmission is dangerous (potentially explosive areas), such as chemical storage facilities or grain elevators. Antenna System & Supplies Inc.'s TRJ-89 jammer comes with its own generator that can block cellular communications within a 5 mile radius.
The company uses phone jammers to stop corporate espionage by blocking the transmission of voice and photos from camera phones. On the more suspicious side of the legality, there are rumors that hotel chains will install jammers to prevent guests from using cell phones and force them to use high-priced indoor phones.
The actual range of the jammer depends on its power and its local environment, which may include hills or walls of buildings blocking the jamming signal. Low-power jammers can block calls within a radius of about 9 m (30 feet). Higher wattage units will create a unitless area as large as a football field. A device used by law enforcement can interrupt services 1.6 km from the equipment.
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