... ,suit for prison,jail room,small room,very secretly Pinhole Style Microphone,Omni Directional, Monitor Range 10-30sq.m ... microphone.*Low noise, Low echo, clear speech, low price.*Built in digital audio disposal circuit , two step dynamic de-noise disposal ... -concelling appearance design, eliminating echo in big hall.*0.8mm pinhole design, clear picking voice.*Pinhole style, little volume, suitable for ...