Brand new, unopened. The auto-dimming function automatically adjusts the clock's brightness to match the room's light level. You can also adjust the brightness manually. There are 3 levels of dimming. You can choose the brightness that suits you. Even when the screen is off, the alarm function will work. You can choose the time display format (12-hour or 24-hour). The alarm clock runs on the included USB cable. When the USB cable is disconnected, the clock will not light up at all. If batteries are added, the settings are saved, and when the USB cable is reconnected, the clock will resume operation and display the correct time.