Bluetooth tape converter. (1) pairing device number (BT-002): can only be paired with one mobile phone at a time. If you want to change to another phone, just disconnect the previous one and re-pair the new phone. (2) automatic pairing: if you have successfully paired with the phone, the next time you pair, please turn on the Bluetooth of the phone in advance, and then turn on the Bluetooth cassette adapter, which will search for the Bluetooth of the phone and pair automatically. (3) whats in the Bluetooth cassette box: a Bluetooth tape converter and USB charging cord. (4) when playing when charging, the current of individual models will interfere with the sound quality. (5) this product has many functions, if you really feel that it is not smooth to use, you can send an email, the seller will help you solve all the problems.