... automatically, protecting rear devices*Echo-concelling appearance design, eliminating echo in big hall.*0.8mm pinhole design, clear picking voice.*Pinhole ... cable, 4 core phone line, network twist line, etc.*Built-in over-loading protection and lightning proof circuit.*Pre-amplifier, directly ... PVCSize 60mm × 22mmWeight 30gStandard CE I.TRADIO hidden,mini,built-in wall Audio Surveillance Microphone