[SGVLUG] Can I Hear An Indication if the Monitor is on or off?

[Dan Kegel via SGVLUG]

You might also try ddcutil, an alternative to ddccontrol.

Here's how it's supposed to work according to
https://superuser.com/questions/648805/is-it-possible-to-power-on-off-a-monitor-using-the-computer/648817
(assuming just one monitor):

--- snip ---
# Show the monitor's declared capabilities.
# But be warned, his is often out of sync with the actual capabilities
ddcutil capabilities

# Show documentation for VCP feature xd6.
# This is no guarantee that feature xd6 is implemented for a
# particular monitor, or that each of the arguments is implemented:
ddcutil vcpinfo d6 --verbose

# Turn of the monitor (assuming everything is implemented)
ddcutil setvcp d6 5

# This typically would turn the monitor back on, but that assumes that
# the monitor is responsive and that argument 1 (DPN On, DPMS Off) is
# implemented
ddcutil setvcp d6 1
--- snip ---

But evidently i2c is a hairy interface, see e.g. http://www.ddcutil.com/nvidia/