... , Low echo, clear speech, low price.*Built in digital audio disposal circuit , two step dynamic de ... eliminating echo in big hall.*0.8mm pinhole design, clear picking voice.*Pinhole style, little volume, suitable for ... core phone line, network twist line, etc.*Built-in over-loading protection and lightning proof circuit.*Pre- ... I.TRADIO pinhole,hidden,mini,built-in wall Audio Surveillance Microphone