?WARM UP?Only 1 device can be paired at a time, it does not transmit to multiple devices; it can only work as a Transmitter or as a Receiver. If have hum when using it, try to plug it into a power bank which will provide enough power to work. For any question, please feel free to contact us!. ?Lightweight&No Battery?Bluetooth audio only weights at 5.4g, it is small, lightweight, space-saving, easy to carry. It is power by USB- No battery, no need driver, plug it into the usb port and it can work all the time.Very easy to use thanks to the mode switch button, simply press the button to change working mode( Red light on TX , Blue light on RX). ?Handsfree Calling?Built-in with microphones, Bluetooth car aux receiver allows you to enjoy phone calls with hands-free calling straight through the car's speakers. With noise cancellation techology, it filters out road noise, gives you clear, crisp sound for hands free calls. ?Low Latency&Bluetooth V5.0?With Low latency technology, Whether you are playing video games or watching movies, you'll experience high quality sound without audio and video to be out of sync issue. Bluetooth 5.0 technology ensures stable connection and fast transmission with working range up to 33ft without obstacles. ?Bluetooth Transmitter&Receiver?This Bluetooth adapter can be used as a transmitter with red light on for TV, PC, airplane, after connected with BT headphone/speaker/sound bar,you can watching TV, play games without disturbing others , or as a receiver with blue light on for car/home stereo, speaker, wired headset for wireless music streaming or handsfree calls.