The US Federal Bureau of Prisons recently ran a test for jamming contraband cellphones in a South Carolina state correctional facility. “Micro-jamming,” or disrupting phone signals within a very precise area, was tested in a federal prison last year. But this test signaled that state prisons — which generally don’t have the authority to mess with phone signals — could be on their way to using the technology.

The test was held last week at the maximum-security Broad River Correctional Institution in Columbia, South Carolina. According to the Associated Press, it lasted five days and involved jamming signals in a housing unit. The National Telecommunications and Information Administration (NTIA), which oversaw the test, will analyze the results and release them in a report.

A new bill would let state prisons jam signals

Corrections officials say that contraband phones are a major issue for prisons, citing cases like the shooting of corrections officer Robert Johnson, who nearly died after a prisoner ordered an attack on his home using a smuggled cellphone. Micro-jamming presents a possible solution, but because of FCC regulations, only federal agencies can legally implement it. And federal prisons hold just a fraction of America’s 2.3 million prisoners, while state prisons hold more than half.

Those rules might be changing, however. Last month, the Senate and House of Representatives introduced bills that would let state prisons jam signals. (In this case, South Carolina Corrections director Bryan Stirling was apparently deputized as a US Marshal, giving him federal authority.) And the FCC has previously loosened restrictions on managed access systems — small-scale cellular networks that can block devices from making calls or using mobile data, but don’t outright jam all wireless access.

However, one commissioner expressed concern that prisons could pass on the costs of these systems to inmates’ families. Critics of jamming say that opening up the rules could create a “slippery slope” to letting jammers proliferate outside prisons, and that imprecise jamming could block legitimate calls outside the prison — although micro-jamming promises to make that problem less likely.

The Federal Bureau of Prisons ran an earlier test of micro-jamming last year at a federal prison in Cumberland, Maryland. The NTIA reported that jammers could disrupt the signal within a prison cell, but keep network access available just 20 feet away — a result that the US Department of Justice called “promising.”