The xscreensaver man page says: POWER MANAGEMENT Modern X servers contain support to power down the monitor after an idle period. If the monitor has powered down, then xscreensaver will notice this, and will not waste CPU by drawing graphics demos on a black screen. An attempt will also be made to explicitly power the monitor back up as soon as user activity is detected. It lies. It still runs while X has put the monitor into standby. Taking an xwd confirms that the module really is displaying - it's not just that the check for DPMS is done in the submodules rather than the xscreensaver process. passion /home/dwmw2 $ ps axf | (sleep 1 ; grep --after-context=1 xscreensaver) 1311 ? S 0:01 xscreensaver -no-splash -timeout 10 -nice 10 3404 ? SN 0:02 \_ penetrate -root passion /home/dwmw2 $ xset q | grep --after-context=1 DPMS DPMS (Energy Star): Standby: 0 Suspend: 0 Off: 1200 DPMS is Enabled Monitor is Off passion /home/dwmw2 $ On a desktop machine, this is harmless enough - aside from making me think X had crashed because it was taking 99% CPU. On a laptop where we actually want to conserve power, it's more important. It shouldn't matter, but the X server is somewhere between 4.0.1e and 4.0.1f on SMP x86.
This shouldn't happen anymore witn 3.29-1 or later, as xscreensaver took over doing DPMS stuff...