For universal wireless transmission of Bluetooth signal sources such as smartphones or tablets to any car radio. One-button function: answer or end calls or redial the last number. Direct MP3 audio playback via the integrated micro-SD card or USB slot. Signals are transmitted wirelessly to the tuned FM frequency (manually adjustable on the transmitter) of the car radio. The device always remembers the last used frequency. Modulation type: FM. Power supply via integrated cigarette lighter plug. USB-C output 2.1A/5V for charging mobile devices.