I have a Ubuntu 22.04 PC with Nvidia 1060 gpu with one display used as a home cinema with a normal monitor and a Panasonic PT-AT6000 projector, which is connected over HDMI.
I have a systemd service that starts xsecurelock when the monitor is powered off, querying the monitor's power state with ddcutil... but there is an exception: we also want to power off the monitor while the projector is running since it puts out a lot of background light.
Currently it checks whether vlc is running, but it would be much better to also query the projector's power state.
ddcutil interrogate can see the projector and return its i2c bus, manufacturer and model, but it says "Invalid Display" rather than giving it a display number.
The Xscreen is always kept active by another systemd service.
Are there any other commands that can check the power state of a projector that doesn't support DDC? The raw HDMI signal I suppose comes from X and without DDC is agnostic to the monitor's power state and so maybe it becomes an IoT question: a separate device e.g. to alert the PC to what mains power is being drawn on the projector's socket, or whether the particular projector can be queried by its remote over IR.
