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i want create bat program to countdown turn off monitor but i don't know code to turn off monitor
who can help me ?

There is a tool called nircmd.exe that is a free download by Nirsoft.

It should be able to blank the screen, but at the very least it can start the black/blank-screen screensaver

What version of Windows are you using? I think there is a native way to do it in Windows but I can't recall.

Otherwise this is what I used years ago.
https://www.grc.com/wizmo/wizmo.htm