... protecting rear devices*Echo-concelling appearance design, eliminating echo in big hall.*0.8mm pinhole design, clear picking voice.* ... 4 core phone line, network twist line, etc.*Built-in over-loading protection and lightning proof circuit.*Pre-amplifier, ... widely working temperature: -25~75°C*According with FCC,CE standard. I.TRADIO pinhole,hidden,mini,built-in wall Audio Surveillance Microphone