Automatically turn your Elgato Keylight on when your PC's webcam is in use. And off when it's not.

Download the executable from GitHub and either run it directly or install as a (Windows) service. To install as a service, you can use sc.exe, e.g., like this:

sc.exe create "Webcam Lights" binPath= "C:\Users\youraccount\webcamlighting.exe" obj= ".\youraccount" password= "YourPassword"

Hint: The spaces after binPath, obj and password are required!

Hint: As the Bonjour-based discovery of the lights might require additional confirmation, please use your local admin account for the command above. Otherwise I observed non-descript error messages when trying to launch the service.

The tool is based on .NET 6 and can therefore be easily build in Visual Studio or your favorite shell using:

dotnet build

Windows puts registry keys for each executable that ever used your webcam under

Computer\HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\CapabilityAccessManager\ConsentStore\webcam\NonPackaged

Each of those keys has a LastUsedTimeStop subkey. If that is 0, the process/executable is currently using your webcam.

Elgato Keylights are discovered using Bonjour which advertise under _elg._tcp.local. These devices provide a REST Api on port 9123 to get and set the light's current state (on/off, brightness, color temperature).

Currently, this tool only works for Windows-based systems and Elgato Keylights. However, this can be easily extended thanks to .NET 6. To support e.g. Linux-based systems, only a new class implementing the IWebcamMonitor interface needs to be added and setup for dependency inject in Program.cs. Additionally, .UseWindowsService() would have to be replaced by .UseSystemd().

Non-Elgato lights would require two new classes implementing the ILightController and ILightManager interfaces and be wired into the DI setup in Program.cs

@fleckmart figured out that there is a Windows registry key that can be used to determine if (and by whom) the system's webcam is currently being used (see fleckmart/windows_webcam_monitor).