Large LED display, in order to save energy, the display will light up when there is a sound or action, and will not light up at other times. To keep the light on, keep it plugged in at all times. USB powered and built-in backup battery, for your convenience, we provide a USB charging cable for our smart clock, built-in coin-cell battery to save your clock settings in case of power failure; time display supports 12 hours and 24 hours Format USB charging port: The integrated USB port charges compatible smartphones and other devices while you sleep. Power Supply and Backup Battery: Plug in the DC adapter to power the clock. The coin cell battery will not run the clock, but will retain the time and alarm settings in the event of a power outage. The PXCL team is at your service and we hope you enjoy your life!