The move is part of efforts to clamp down on illicit handsets, which fuel violence and drug dealing behind bars, officials say.
Prison staff are using specialist detection equipment to pinpoint where inmates are using illegal mobile phones down to the precise cell, the Ministry of Justice has said.
It is hoped the new technology will clamp down on illicit handsets, which officials say can be used by prisoners for purposes including drug supply, maintaining outside criminal networks and terrorising victims.
Justice Secretary David Gauke said: «As criminals look for new ways to smuggle contraband into prisons, it is vital that we stay one step ahead, and this kind of technology will help prevent them operating from their cells.
«This is vital to ensuring prisons are places of safety and rehabilitation, where offenders can turn their backs on crime for good.
