I have a new monitor that's notoriously prone to burn-in ...  This is an IPS monitor, and none of us thought burn-in even existed anymore.  But I don't think this is quite the same as what it was with plasmas - in this case, I think the "burn-in" lasts a matter of hours rather than being permanent?  I'm not sure because I don't care to experiment.  Yes, I knew this before I bought the monitor, but it's other advantages outweighed this problem.  And yes - it's an incredibly stupid problem to have with a monitor where things stay in the same place for hours, months, and sometimes years.

So one of the computers I attach to it (a middle-aged Chromebook) has Debian stable installed, and I'm running Fluxbox on it.  I use this:

    $ xset +dpms
    $ xset -q
    ... # DPMS confirmed on
    $ xset dpms 240 1800 1800

To turn on DPMS and set the time-outs.  But ... every time the screen blanks, it apparently disables DPMS again.  This can be confirmed with 'xset -q' again, which now says "disabled."  Is this a system setting or service, Debian or Fluxbox or something else that resets itself every time DPMS is activated?  I have no such problem under Fedora 26/Openbox.