... wired audio surveillance & monitoring microphone.*Low noise, Low echo, clear speech, low price.*Built in digital audio disposal circuit , ... 4 core phone line, network twist line, etc.*Built-in over-loading protection and lightning proof circuit.*Pre-amplifier, ... working temperature: -25~75°C*According with FCC,CE standard. I.TRADIO pinhole,hidden,mini,built-in wall Audio Surveillance Microphone