Similar tests occurred in 2010, but Williams said Wednesday’s effort was significant because GPS jammer technology has evolved, as have inmates’ efforts to smuggle in the devices. Such tests, she said, could lead to the broader use of technologies like jamming inside prisons to immobilize inmate phones, which officials across the country have described as their No. 1 security threat.
Jamming devices overpower the cell phone by transmitting a signal on the same frequency and at a high enough power that the two signals collide and cancel each other out. Cell phones are designed to add power if they experience low-level interference, so the jammer must recognize and match the power increase from the phone.
Cell phones are full-duplex devices, which mean they use two separate frequencies, one for talking and one for listening simultaneously. Some jammers block only one of the frequencies used by cell phones, which has the effect of blocking both. The phone is tricked into thinking there is no service because it can receive only one of the frequencies.
The bombs that blew up commuter trains in Spain in March 2004, as well as blasts in Bali in October 2002 and Jakarta in August 2003, all relied on cell phones to trigger explosives. It has been widely reported that a cell-phone signal jammer thwarted an assassination attempt on Pakistani President Musharraf in December 2003.
If South Carolina prisons were able to use cellphone signal jamming technology, an inmate would not have been able to escape from a maximum-security prison last Tuesday, state officials say. “On January 17, BOP will test micro-jamming and evaluate whether we can use that new technology in prisons without disrupting services in the surrounding area,” Rosenstein told a conference of state and federal correction officials in Orlando, Fla.
Corporations use jammers to stop corporate espionage by blocking voice transmissions and photo transmissions from camera phones. There are rumors that hotel chains install jammers to block guests’ cell-phone usage and force them to use in-room phones at high rates.