Now you control the radio program. Simply connect your smartphone to this small FM transmitter, and your music will be available like a regular radio station. Additionally, the transmitter has a micro-SD card slot, allowing you to transfer music stored on a micro-SD card directly to your car radio. There are also two USB charging ports available for smartphones. Extra power for your smartphone: the RF-CAR-100 features two pure USB charging ports with a total of 3.1 amps of charging power.