Styjun

Have a large amount of Win7 video devices distributed among several different locations in a healthcare setting. Sometimes the need is dire and they be used in a moments notice. Each device connects via HDMI to a wall mounted TV.
One pain point is that sometimes people will disconnect the HDMI cable from the Win7 computer to plug into their own personal devices which violates policy. They will not reconnect the cable which causes problems when the device needs to be used next. It has caused delays in care.
The past week i've been working to write a small app (preferably a service at system level) that will detect when display is no longer connected to PC then trigger action (e.g. EventLog entry, send email alert, etc). Unfortunately all my attempts have been met with roadblocks. Looking for ideas.

I've spent quite a bit of time researching ways or "hooks" that I might be able to surface within Windows that I can trigger off of. I found that there are native classes (DeviceWatcher, WindowsDeviceEnumeration, etc) that might help this work, but unfortunately they're not Win7 compatible.

I did create a c# console app with event handler for SystemEvents.DisplaySettingsChanging and this works just how I would like! I can disconnect the monitor and it will send an alert email and write an event log entry (which we can monitor with 3rd party tools and alert, create ticket, etc). While this console app works great, I need it to work more as a hidden background service. I created a Windows Service with the same functionality, but I found that event handlers can be tricky in Windows Services. I could never get the EventHandler(SystemEvents_DisplaySettingsChanging) to trigger when in Windows Service Mode. I've since found that EventHandler DisplaySettingsChanged is a user level event and will only work for current user and not system level when run as a service.

I've tested various methods of unplugging monitor and looking for ways for windows to report "No Monitor). I've tried WIn32_PnPEntity Class as well as Win32_Video* classes and they will all report that monitor is OK status even though it isn't connected.

I did find that I can literally watch device manager while disconnecting a monitor and see the monitor disappear from Monitors tab. There has to be some way I can hook into this.

I'm thinking I can run a windows service with a timer that will check this hook. If monitor connected, do nothing - if NOT connected, do action (send alert, write event log entry, create ticket, etc.)

Ultimately I expect to have a Windows Service with timer that will run in system mode which basically re-runs a check like this this:
If monitor connected, do nothing.

If no monitor connected, send alert, create ticket, create eventlog entry, etc..

I've spend a good chunk of time on this and I have to present findings 3/28.

Any help appreciated. Thanks!

I explored WM_DEVICECHANGE and WM_DISPLAYCHANGE but I just couldn't get either to work as I needed and I was running out of time.

I need more time to figure these out (and capturing windows messages in general) in the future.

However, I was finally able to find the right hook to achieve my objective.

The challenge I was having was that no matter what class or assembly I used to detect monitor connection, I was always returning at least one display even though it was physically disconnected.

Tinkering in PowerShell, I found that using WMI and Win32_PnPEntity, I could pull the display info and if NO displays were connected, the DeviceID would always return DisplayNVD0000SomeGuid. When 1 or 2 monitors were connected the DeviceID's would be a hex variation replacing the zeros after NVD (ex. DisplayNVD39E4someGUID).

Knowing I could count on getting a deviceID of DisplayNVD0000 when no monitor was connected I build a windows service, with a timer using ManagementObjectSearcher and Win32_PnPEntity. Timer runs every 10 minutes then executes a check.

If finds no display physically connected, it will fire an event log entry which can be monitored with an external monitoring tool (Xymon, Nagios, etc) and an alert/action can be taken to ensure it gets corrected.

I tested with an HDMI monitor. Tested with monitor in powered off condition and with monitor source changed to another input condition (Not HDMI) and the only condition where I could get the alert to trigger was when cable was physically disconnected from PC, which is exactly what I wanted.

Theres more than one way to skin a cat. I know there are other devs out there that could've whipped together an elaborate working solution in a matter of a minutes. Considering the amount of cumulative screentime in C# over my career (not a lot, comparatively), I feel good about this small victory.

Hopefully this might help someone in the future.