• Power Source: Rechargeable lithium cell operation (3.7V / 5V depending on model variant like SD-7SU or SD-7SBU).
• Audio & Media Options: Built-in music, alarm siren, voice recording/playback, U-disk/USB support, MP3/WAV playback, and Bluetooth connectivity (on the SD-7SBU model).
• Design: Lightweight and portable handheld build with a comfortable gri