[gpm] How to manually turn off the screen?

[Kevin Ross <kevin familyross net>]

 Hello,

I used to be able to turn off the screen with "xset dpms force off".  
But now that doesn't work, the screen only stays off for a few seconds.

The Debian BTS has an open ticket on this 
(http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=552506), and they say 
we shouldn't use xset, because it will conflict with GPM.  They say send 
a dbus message to GPM to turn off the screen.  So some Googling gives me 
this command:

dbus-send --session --dest=org.gnome.PowerManager --type=method_call 
/org/gnome/PowerManager org.gnome.PowerManager.setDpmsMode string:off

However, I get an error that setDpmsMode is an unknown method.

So my question is, what is the proper way to programatically turn off 
the screen?

Thanks!
-- Kevin