Here are a few results of installing batteries or plugging in: 1. Battery only --- The clock and alarm will run, just automatically enter the power-saving mode after no operation, i.e. the screen will turn off and enter the background operation. 2. Plug in the USB cable only --- the clock and alarm will run normally, the screen will be on all the time, but there is no time memory function, once the power is off and then plugged in again, you need to reset the time. 3. Install the battery and insert the USB cable -- the clock and alarm will run normally, the screen will be on all the time, and the clock will have a memory function, once the power is off and connected again, you do not need to reset the time. So if you need the screen to stay on all the time, you can plug in the USB cable only or plug in the USB cable and install the battery.Please note that the two dots in the middle of the digital alarm clock will flash to indicate that time is ticking forward, as well as to differentiate from the date display. Please refer to the video operation on the instruction manual to use it with half the effort. Please note that the color of the digits is fixed and cannot change. Desktop alarm clock ---- clock (12/24H), alarm clock (alarm clock has three modes, The clock is accompanied by an incregly rapid alarm, and stops after 60 s of ringing.), calendar, temperature (Celsius/Fahrenheit) . The light blue digital alarm clock has two display modes, one is to display the time only, and the other is the time/date/temperature are showed in turn, The time is displayed for 10 s -- the date is displayed for 3 s -- the temperature is displayed for 3 s. Adjustable brightness, 3-level manual adjustment and automatic adjustment. You can set the time of automatic mode (night mode) according to your work and rest rules. Whether it is day or night, you can clearly see the time, even at night, there will be no dazzling lights, and it can even be used as a small night light, guard your night. (Note that in bright light, numbers will not be displayed clearly.) Long press LIGTH/SNOOZE for 5s, the screen will light off. Bedside alarm clock, corded power operated, memory function. Alarm clock is powered by cable, so you must use the USB cable (no adapter). When you install 3 AAA batteries, the alarm clock will have a memory function. If you suddenly unplug the cable power, the memory battery will remember the time and the screen will enter sleep mode. You can wake it up by making a sound, but the screen will go back to sleep after 10 seconds until you plug the cable. The 6.5 inch small screen has 2 inch high digits. Although it has a small screen, the high colored numbers make the small desk alarm clock clearly to read, small and light. The colorful numbers are eye-catching. The measured dimensions of the product are 6.3"W x 2.36"H. Adjustable 12/24H. (Note that in bright light, colored numbers will not be displayed clearly.).