The Fm Transmitter Is A Multifunctional Device. The Applied Bluetooth Technology Enables Wireless Connection Of 2 Phones At The Same Time And Playing Music. Just Connect The Phone To The Transmitter And Then Adjust The Appropriate Radio Frequency. The Usb Ports Allow You To Charge Your Devices (Max. 3.4 A) As Well As Play Music From Your Flash Drive. Due To The Microsd Slot, You Can Play Music From Your Portable Memory Card. The Built-In Microphone And A Special Call Answering Button Function As A Handsfree System For Making Calls. The Device Can Also Serve As A Voice Amplifier For Car Navigation. All Necessary Information Is Displayed On The Built-In Led Display.