This item is a car kit, which including FM transmitter and two USB charging ports. Plug the item into your car cigarette lighter, then it would be power-on automatically. It is compatible with most enabled devices. Features - Color: Black. - Material: ABS. - Size: About 3.4 * 7.8 cm/ 1.34 * 3.07 inch(L*W). - Version: V2.1, Support A2DP, AVRCP, HFP. - Wirelessly transmit phone call from mobile phone to the car FM stereo system. - Switch to hands free model automatically from music playing status when receiving call. - With A2DP function, stream music from device to car's FM stereo system. - Supports music playing from USB disk. - Supports MP3/WMA format files. - Draws power from the cigarette socket in the car (DC 12-24V). - Dual USB outputs 5V/3.4A, charges iPhone, iPad, and other devices - Full 206 channels optional from 87.5-108MHz. - LED display the number. - With voltage dection to remind your car battery health status. - Incoming call number announcement. - Redial the last call. Update content - 4.2, better compatibility and less packet loss than 2.1. - Orange color display lamp enhances visuality. - Dangling transmitter enhances reduction degree basic sound pickup effect that creates more authentic voice. 1. Question: Unable to Connect to Answer: unpair all the connected on the mobile phone, and then reconnect 2. Question: Unable to set the FM Answer: Long press the phone button for 1 sec, press the up and down volume button to adjust to the same channel as the car radio. 3. Basic Operation for Connection: Delete pairing history. If the pairing code fails, search for links again. And some mobile phones, like Huawei, might not be able to successfully scan out the pairing code for the first time, you need to refresh to scan out the pairing code.