For universal wireless transmission of Bluetooth signal sources such as smartphones or tablets to any car radio. Make calls easily with the integrated hands-free system. 1-button function: answer/end calls or redial the last number. Direct MP3 audio playback via integrated micro SD card slot. Signals are transmitted by radio to the tuned FM frequency (set manually on the transmitter) of the car radio. The device always memorises the last frequency used. When an incoming call is received, the device automatically switches from music mode to hands-free mode.