Small design Bluetooth FM transmitter for smartphone, 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: Listen to music on Bluetooth devices via FM signal or transfer music from MP3 players, old speakers, tablets, etc. to car audio system via AUX cable; it also supports MP3, WMA, WAV, and other formats from a USB drive (up to 32GB). Hands-free car kit: High-performance microphone with noise reduction technology (CVC) allows clear voice communication. One-button control to answer, reject, redial, or end calls. Seamlessly switch between incoming calls and music playback. Supports voice navigation from mobile phones for safer driving. Dual USB interface: The car Bluetooth audio transmitter supports charging two devices simultaneously. The 2.1A port with lightning bolt icon enables fast charging. The 1A port with music icon can also read data from a USB flash drive. General compatibility: Bluetooth FM transmitter for car works as a hands-free device compatible with all Bluetooth-enabled phones and audio players. The AUX input port allows connection to non-Bluetooth devices using an AUX cable, such as MP3 players, MP4 players, CD players, or tablets without Bluetooth functionality.