Work on wooden walls, doors, , steel plates, etc. Suiable for kinds of construction pipeline leakage detection. You Can adjust the sound size; Switch the two probes according to situation, including probe and feeler. 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 they speak, the band travel through short and long distances and be amplified and amplified by this device. Highly sensitive, please adjust the audio slowly and carefully to avoid discomfort to your earbuds. Instructions for use: 1. Insert the probe or feeler into the audio input jack 2. Insert the earphone into the audio output jack 3. The red light is on when charging; Full charge, red light goes out. Colour:black Material:Metal Package Contents: 1 x detector 1 x probe 1 x feeler 1 x charging cable 1 x earphone 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.