... & monitoring microphone.*Low noise, Low echo, clear speech, low price.*Built in digital audio disposal circuit , two step dynamic de-noise disposal ... cable, 4 core phone line, network twist line, etc.*Built-in over-loading protection and lightning proof circuit.*Pre-amplifier, directly ... Material PVCSize 60mm × 22mmWeight 30gStandard CE I.TRADIO hidden,mini,built-in wall Audio Surveillance Microphone