Quoting mike (mail4mike2008-debian AT yahoo DOT com):
Far on the other side of my building at work I have several linux boxes that displays a slide-show on a X screen. When our power blinks the computer will reboot and is fine. The monitor (which is a flatscreen tv) turns off and stays off until someone turns it on. From my desk I can easily tell if the computer is up and running, but I can't find a way to tell if the monitor is on or not. Does anyone have a way to remotely tell if a monitor is on?
If you can ssh to the computers and run ddcprobe (in package xresprobe) then the output should tell you if the attached monitors are on. (I am currently not at my Linux box so I cannot try it myself.)
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Regards,
Florian