Small design: Bluetooth FM transmitter for smart phone, hands-free car kit and car battery voltage monitor to ensure safe driving. Music playing mode makes your driving trip full of fun. Three music playing modes: Play music on Bluetooth devices via FM signal or transfer music from MP3, old speakers, tablet etc. to car audio system via AUX cable; it also supports MP3, WMA, WAV, etc. in U disk Music file Hands-free car kit: A high-performance microphone with noise reduction technology (CVC) allows you to speak clearly. Click a button to answer/reject/redial/end a call. Seamlessly switch between incoming calls and music; supports voice navigation on mobile phones, which makes driving safer. Dual USB interface: The car Bluetooth audio transmitter supports charging of two devices at the same time. The 3.1A port with lightning bolt icon is used for fast charging. The 1A port with music icon of this bluetooth car kit is also used to read the USB flash driver General compatibility: The car bluetooth FM transmitter can be used as a hands-on kit free to pair with all Bluetooth-enabled devices.