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On Friday CellAntenna demonstrated it could jam mobile phones within a 1000 square meter area within a prison, without noticeably affecting those passing. This opens the door to widespread adoption of the technology.

The test took places at the Lieber Correctional Institution, at the request of Jon Ozmint and in the presence of representatives from the a US Senators office, as well as the Department of Corrections from Arkansas and Texas and the state governor. An area of the prison extending about 1000 square meter was jammed and the audience was invited to wander in and out of the jammed region to see how well-defined it was.

Howard Melamed, CEO of CellAntenna, told The Register the test wasn't for their benefit - he already knows the technology works - but the various legislative bodies need convincing that local residents won't be affected and that claims from the mobile trade body, the CTIA, are groundless. There is also the question of legality - in the US only federal bodies are allowed to jam radio transmissions, regardless of the circumstances, something against which Howard has fiercely complained:

"We believe we are within our rights, as an American company protected by the first amendment, demonstrating our technology." He also pointed out that only the person actually flicking the switch could be accused of illegally operating a jammer - and then declined to tell us who that was.

Alternatives to jamming have been considered but inevitably end up costing a lot more, according to Melamed. Fitting fake base stations or routing calls through a proxy both require maintenance - listening in to calls particularly so. Tracking technology can be accurate but would require frequent cell visits and more searching of inmates as they denied knowledge of the tracked device.

Fitting a jammer is a one-shot deal with a price tag of around $150,000 to cover the 50 per cent of an average prison where jamming would be most needed. That price includes a central control and monitoring system.

But before that can happen the FCC needs to sanction it, and the network operators will fight tooth and nail against that through the CTIA. Officially the arguments are that jamming will interfere with legitimate users, and that greater use of jammers will lead to their wider availability, but Howard sees another motivation:

"According to our estimates [the network operators] are making $25-$30K a year, per prison, and there are 700 prisons in the USA", he told us. "Why else would they have [radio masts] pointing at prisons?"

With careful radio mapping and directional antennas CellAntenna reckons it's perfectly possible to jam signals within a building - the company only jams the base-station-to-mobile portion of the signal - while having no effect outside it. Anyone who's had to hold their mobile up to a window will know how effective walls can be at blocking signals, and that applies equally to the jamming signal.

Certainly the traditional UK prison walls should prove effective, and CellAntenna and Melamed have been hanging around in the UK talking to prison governors who are desperate to get the technology, but the UK Home Office is as reluctant as the FCC to permit the use of jamming technology.

With jamming technology already being used by criminals before they're caught (in Canada at least) the availability argument doesn’t really wash, and if demonstrations like the one on Friday continue to prove the technology can work without upsetting the locals then there seems little reason to continue to allow lags to phone home from the comfort of their cells. ®

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