The DIY bone conduction speaker uses 5V power supply. When connected to a mobile phone's Bluetooth to , the resonant speaker emit mechanical vibration and make sound when in contact with an object. The quality of the sound is directly related to the size and hardness of the cavity of the object in contact, and can be used as a hidden speaker with a wide range of uses to unleash imagination. After the Bluetooth board is powered on, it is forbidden to come into contact with conductive objects to avoid short circuits and burning out the chip. When using, do noytt touching the components on the Bluetooth board with your hands. undergo testing before shipment. Color: As Shown Material: PC+Metal Package Contents: 1 x 4Ohm 5W diy speaker Only the above package content, other products are not included. Note: Light reflection 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.