Published: Thursday 15 October 1998

Cellphones are not just a public nuisance - they are also used by lookouts to warn criminals when the police are near. Now Deropa of Boksburg, South Africa, is patenting a transmitter that jams cellphones. All cellphones continually transmit and receive coded signals, with which they communicate with the network base stations. If these signals cannot get through, the phones cannot make or receive calls. By broadcasting low-power noise, the transmitter blocks these signals, preventing the cellphone from working.

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