Work on wooden walls, doors, windows, steel plates, etc. Highly sensitive, please adjust the audio slowly and carefully to avoid discomfort to your earbuds. The audio gadget works by amplifying the vibration of audio. When people chat in the room, their voice is only a band, and according to the size of the voice they speak, the band will travel through short and long distances and be amplified and amplified by this device. Colour: Black material: metal Package Contents: 1 x Detector 1 x USB Cable 1 x Circular probe 1 x Needle probe 1 x Headphone 1 x Chinese and English manual Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.