1. Turn on battery test voltage.Car Bluetooth compatible MP3 supports hands-free calls, built-in high-sensitivity microphone, noise floor and suppression. 2. Support TF card expansion to play MP3/WMA format music; Comes with its own car charger, which can charge handheld terminal devices. 3. Supports Bluetooth compatible hands-free, built-in microphone, making answering calls convenient and safe; caller ID.Automatically reconnect and enter pairing state after powering on; 4. Call noise processing , wind noise suppression, full-duplex call technology; 5. Support the A2DP function of mobile phones, connect to Bluetooth compatible and directly play high-quality mobile music; support lossless audio decoding, high-resolution, high-performance stereo, and lossless music formats such as WMA, APE, FLAC, and WAV. AVX port output and input.Automatically detect car battery voltage, provide voice reminder, and support instant voltage viewing Bluetooth compatible smart MP3 player, supports mobile phone/network/all kinds of music APP software playback Technical Parameters: Input voltage: 12-24V Output voltage: 5V+/-0.25 Output current: 1000mA (maximum) Short circuit protection current: 2.4-3 Bluetooth compatible version: V5.0 + Frequency: 20 hours ~ 20KHZ Sensitivity: -42dB+360dB/3dB Voltage: 5V+/-0.5 Working current: 45mA (large) Standby current: 25mA (high) Frequency: 2.402~2.480GHz Effective distance: 5 meters Sensitivity: -92dBm RF output: 4 dBm Frequency: 87.5MHz--108.0MHz Transmit power: 87 dBuv / 107 dBuv Effective distance: 5 meters Material: abs colour: As Shown Package Contents: 1 x Car Bluetooth MP3 Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.