The Pioneer DEH-S4250BT is a single-DIN CD receiver that features dual Bluetooth connectivity, compatibility with the Pioneer Smart Sync app, and a variety of audio customization options. It also includes a front-facing USB port that can quick-charge Android phones. 
Key features
Dual Bluetooth: Connect two smartphones simultaneously for hands-free calling and wireless audio streaming. This allows two users to answer incoming calls from either phone and stream music from one.
Pioneer Smart Sync: This app-based technology links your smartphone to the receiver, giving you control over audio settings, navigation, and other features. Through the app, you can access an expanded 31-band graphic equalizer.
Spotify control: The receiver supports Spotify, allowing you to control the app on your smartphone directly from the head unit's interface.
Audio quality and customization: The DEH-S4250BT has a built-in MOSFET amplifier with 50W x 4 output. It also includes a 13-band graphic equalizer (upgraded to 31 bands with the Smart Sync app) and a Dynamic Bass Enhancer feature.
Media playback: The unit features a CD player for traditional playback and supports a wide range of digital formats, including FLAC, MP3, WMA, WAV, and AAC, via the front USB port.
Karaoke Vocal Cancel: This feature can remove vocals from music played from supported sources like CD, iPhone, USB, and Bluetooth Audio.
Inputs and outputs: For connectivity, the unit has a front USB port, a front AUX input, and two 2V RCA pre-outs for connecting external amplifiers or subwoofers.
Anti-theft security: The DEH-S4250BT includes a detachable faceplate.