Smof Bluetooth CSR4.0 Stereo Music Receiver/Hands-Free Car Kit for Car Audio System with Knob Rotatable Adjustment Built-in Mic/3.5mm Output(Black) Features:It can connect your cellphone with car audio system through Bluetooth;Built-in microphone,You can play music wireless and receive calls with your hands free;Human-centreed design and simple operation Rotatable Adjustment:No other button to control volume or songs.You just need to rotate the product and control everything.You can simply rotate the knob left or right to go to the previous / next song, or rotate & hold the controller a few seconds to decrease or increase the volume Easy to Control:When you start your car,it will power on again and it can connect automatically Hands-free Calling:Built-in microphone,you can receive your calls with your hands free when your are driving;Almost support any Bluetooth capable device such as Apple iPhone iPad iPod BlackBerry Samsung and other Android Smart phones Optional Suggestion:1.The car charger isnt included in the package,you can choose our Smof Car Charger (2.1A/4.2A) as you like.2.Some cars may have the noises caused by Ground Loop ,you will enjoy good quality audio when use with Smof Ground Loop Noise Isolator,it can completely eliminate noise and hum