Suitable for wooden walls, doors, windows, steel plates, etc. Highly sensitive, adjust audio carefully and slowly to avoid earbud discomfort. This audio gadget works by amplifying the vibrations of audio. When people speak in a room, their voice is just a band, and depending on how loud they speak, the band travels short and long distances and is picked up and amplified by the device. Color: Black + Silver Material: Metal Packaging contents: 1* Detecotor1 * USB cable 1* Round probe 1* Needle probe 1* Earphone 1 * Instruction manual only contains the above packaging contents and does not include other products. Note: Light and different monitors may cause the color of the item in the picture to be slightly different from the actual color. The measurement allowance is +/- 1-3 cm.