... Low noise, Low echo, clear speech, low price.*Built in digital audio disposal circuit , two step dynamic de ... devices*Echo-concelling appearance design, eliminating echo in big hall.*0.8mm pinhole design, clear picking ... 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