[Free Switch Between Wired and Wireless] - KZ Bluetooth module is specially designed for Earphones with 0.75mm /0.78mm pins, making the wired headphones become wireless headphones in seconds, and getting rid of the bondage of wire harness. It allows you to switch between wired and wireless according to the needs of different scenarios. It also ensures the sound quality of the original headphones. ( *This product is only for bluetooth upgrade earhook, without earphones.) [High-Fidelity Sound] - Adopting bluetooth 5.4 technology, Bluetooth Module offers you an unparalleled audio experience with faster transmission speed, stronger connection stability. At the same time, AAC advanced audio coding transmission technology to greatly improve the quality of hearing and bring natural and clear sound. [Long Battery Life] - Each earbud can get 6 hours playback from a single charge. 400mAh charging case supports 4 times of recharging for both earbuds, gives up to 30 hours continuous music tim