Mine is even simpler - I just control an off-the-shelf smart bulb via a couple of macOS Shortcuts, which is trivial using Homekit. Those are driven by Hammerspoon which triggers the shortcuts based on the camera events. No custom hardware and like 20 lines of code (not including the shortcuts, I guess). I have the bulb in a normal lamp base outside my door. It's properly event driven rather than polling, too.