... loading protection, Lightning proofAudio Preamp Build-inOutput Connector Power+, Audio and GND Cable 3 x 0. ... rear devices*Echo-concelling appearance design, eliminating echo in big hall.*0.8mm pinhole design, clear picking ... 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