I have much automated, but my favorite is a $20 multicolored hexagon WiFi light with a long usb power cable I nestled along the door frame from power to the light above my wife’s office door. I wrote a swift daemon to monitor her work mac’s camera and microphone usage as well as idle time, and decide whether to set the little hexagon over the door to red, yellow, green, or off depending on camera use, mic-only use, idle under or over threshold, respectively. That way I know whether I can safely interrupt, and with what degree of caution. It’s been a champ, but I did need to modify the code when she upgraded from intel to m1, to listen to camera logging events rather than checking the hardware directly, but other than that it makes me happy every time I walk by it.
Second is more common, but also makes me happy every time: I put a contact sensor on the interior door to the attached garage that when opened quickly turns on the light to the garage, and turns it off a few minutes after that door next closes. It sure beats walking into a dark garage to fumble for a switch.