AP-S Turnstile

The technology behind cell-phone jamming is pretty simple. The device broadcasts a radio signal in the frequency range reserved for cell phones that seriously interferes with the cell-phone signal, resulting in a "no network available" display on the cell-phone screen. The jammer is not target-specific: all phones within the effective radius are silenced, indiscriminately. This countermeasure does not require the brute power of a microwave oven to be effective; international Web sites selling such devices tout radiated power of 20 milliwatts.