2 in 1 Wireless Bluetooth 4.1 Music Audio Receiver Transmitter Adapter Dongle Receiver sensitivity of -90dBm 6-bit DAC over a dynamic range &gt;30dB 2 microphone bias generators and up to 2 analogue Selling Point: Bluetooth 4.1 Chipset(CSR 8670), Simple,Convenient,Durable, Rechargeable lithium battery Send and receive integrated model, the company uses the most high-end chip csr8670 CSR, (containing lithium battery, sustained for 9 hours)