Function: 1. Compatible: audio receiver adapter to easily add BT to car speaker system, home stereo, speakers, wired headphones via 3.5mm AUX jack. Slim design, compact and space-saving. meet your usage needs. 2. 3. NFC function: The sound adapter supports NFC pairing. When pairing, the NFC of the phone is turned on, and the BT 21 will appear when the mobile phone is close to the product. Click to connect and it will automatically reconnect when used again. 4. Easy to use: 2-in-1 audio adapter, one-button control, AUX, RCA connectors. These two interfaces support BT audio receiving and transmitting functions. Plug and play, easy setup, one key operation, clear status indicator. 5. HiFi Sound Quality: The transmitter of the wireless sound receiver adopts HiFi IC decoding to ensure that the BT is not distorted, listening to songs is not blocked, low latency, HiFi sound quality allows you to experience excellent music. Specification: Item Type: Sound Receiver Adapter Material: ABS Transmitter interface: AUX RCA Model: BT 21 Output impedance: 75 ohms Frequency response range; 10Hz - 20kHz IC decoding: for Jerry IC Signal noise: >90 DB Effective open space: approx. 15m/49.2ft BT version: 5.0 Performance: HiFi stereo class Built-in battery type: lithium-ion battery Battery model: 502030 Battery capacity: 200mAh Package List: 1 x BT audio receiver adapter 1 x 3.5mm male to male cable 1 x USB to Type C charging cable 1 x RCA One for two to 3.5mm male cable 1 x Chinese and English manual Receive mode: blue light flashes when the product is turned on for 3 seconds, the BT mobile phone is turned on to search for BT 21, click connect and insert the 3.5mm AUX sound port or RCA cable to connect the speaker and the Host product, then mobile phone and speaker can play music wirelessly. When the product is turned on, BT flashes, the mobile phone's NFC is turned on, and the mobile phone's NFC is in the induction area with the NFC word printed on the product. When the NFC of the mobile phone is detected, BT 21 will appear. Click the connection and insert the 3.5mm RCA cable to connect the speaker with the product host, then the mobile phone and the speaker can play music wirelessly. Transmission mode: when the product host is turned on, the red light flashes, and the BT speaker or BT headset will be automatically connected to play music when turned on.