... , Monitor Range 10-35sq.m,suit for prison,jail room,any small room,very secretly Part of customers: Guizhou Provice prison; Dalian ... voice.*Pinhole style, little volume, suitable for jail room and other small room.*Long-distance transmission, the maximum transmiting distance can reach ... FCC,CE standard. I.TRADIO pinhole,hidden,mini,built-in wall Audio Surveillance Microphone