EASY TO OPERATE: Press firmly against doors, window and wall and adjust the sound with the knob until you hear a clear sound, able to emit sound from wooden wall, bricks, window and doors, effective noise filtering and faster sound detection.SOUND SENSITIVITY: High sensitivity metal alignment with headphones improves sensitivity and sound quality, high sensitivity detects sound from wall, window, doors or armor plate with headphones for clear sound quality.APPLICATIONS : 3.5 mm headphone jack can be connected to display spectrum, voice recorder, transmitter, devices, etc. (not included), also can be plugged into the dual channel line for direct recording, can detect abnormal noises from heating ducts, fire ducts, water pipes, underfloor heating ducts, automobile, home plumbing, and more.WITH CHARGING INTERFACE: Through wall door microphone with charging interface, the built in battery can be charged repeatedly, fully charged once available 5 to m7 hours, machine jack and upward switch knob, easy to use and adjust.STRONG PENETRATION: High sensitivity sensing head using new components and advanced technology, so that the penetration increased by several times, greatly improving the sound quality, carefully and slowly adjust the voice frequency, so as not to cause discomfort to the ear plugs.