MobiFren GBH-S100 Stereo & Mono Bluetooth Headset Mono for call and Stereo with sub receiver for music. Through built-in DSP chip, it optimizes the best sound quality by eliminating noise and echo Natural 3D effect by Mobifren's specialized digital signal process Ultra Power Save Mode: Maximum stand by time up to 6 months Call Lock: Prevent unintentional call by call lock button. Smart Connection: When there is an incoming call, just slide up the MFB button to unlock position to answer Combo: Mono & Stereo Bluetooth Headset. Loss Protection: Twist cap to open and close