Thinking about Samsung's always on display, but you don't have one. No matter what android phone you have, just go ahead with this post.

Warning : Use this only if you are having an AMOLED display. If your phone is a non AMOLED display then it will drain the battery very fast.

Download

Requirements :
AMOLED Display Android Phone

Steps :

Install the app from the above link
Open the app
You will be asked a permission to enable change system settings. Just enable it
Press back and allow the required permissions
Enable glace from the up right corner and turn on drawing over other apps. press back.
Set the settings as you want and change glance type to always on.
Done

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