Always on Display is a free utility app that lets you show basic information on your mobile screen, such as the current time, date, battery level, or notification messages. It does so by black-screening your device, so you can see these messages and notifications on the black screen. 

This application allows you to choose among three clock styles: an analog clock, a digital clock, and a clock with a notification. You can also change the display's background and text colors. You can also set it to show notifications from your apps and battery level. You can even show the time or date in multiple languages.