Features: Built-in microphone, when connected to the mobile phone BT, hands-free calls are supported, which is very convenient to use in the car. BT5.1 technology, lower power consumption, more stable audio signal transmission, the use distance of fewer than 10 meters. There is no built-in battery, and it is powered by a DC 5V USB interface. USB AUDIO OUTPUT MODE-If the device supports USB audio output function, plug, and play, no need for an audio cable. AUX AUDIO OUTPUT MODE-AUX mode requires an audio cable to link the product and audio equipment. With the 3.5mm cable, this Receiver Transmitter adapter can widely be used on your computer, laptop, home stereo system, headphone, smartphone, Mp3 player, CD player, etc. The Mini portable KN318 is just 32mm (1.26) across and weighs only 3.2g (0.11oz), but has got powerful wireless audio streaming capabilities. Note: The USB interface of the device has an audio transmission function, so it can be directly plugged into a USB. The USB interface of a small number of devices may not support or be incompatible, you need to use AUX mode.