What's the context?

US prison officials harness new technology to crack down on contraband cellphones but some still want powers to jam signals

• South Carolina programme shuts off more than 800 phones


• Federal action on broader signal jamming tech seen as unlikely


• Activists raise privacy, rights concerns for prisoners

Digital privacy rights advocates and tech experts say even solutions less far-reaching than full-blown signal jamming - like the South Carolina pilot - threaten to trample on the rights of prisoners by, for example, sharing legally protected information with private phone companies or carriers.

Digital rights groups have long raised concerns over the push for cellphone jamming systems in prisons, describing them as overreach.

Under federal law, state and local facilities are not allowed to use jamming technology, which is opposed by the telecommunications industry amid concerns that it could knock out signals in areas surrounding prisons.

The Federal Communications Commission (FCC), which regulates communications technology in the U.S., has been wary of signing off on full-blown signal jamming but cleared the way within the last few years for states like South Carolina to implement so-called "contraband interdiction systems."

Stirling is convinced signal jamming is a solid option but does not think it will be authorised in state prisons. It is already allowed in federal institutions.

"I would love to get jamming - I don't see it happening, unfortunately," he said.

Asked if the FCC was contemplating changes, a spokesperson pointed to the federal law banning jamming devices.

Albert Fox Cahn, founder of the Surveillance Technology Oversight Project (S.T.O.P.), says both jamming and interdiction systems like the one used in South Carolina are "chilling options" that could have unintended consequences.