I had a customer that desperately needed automation. The house is in the north east and has a nicely finished basement which has electric heat in the Floor. They also have two huge HVAC units cooling the home. The cool air from the AC fell to the basement and then the basement turned on the floor heat and that heated the entire house requiring more AC (Crazy!!)
The solution was to automate the electric floor and the entire house. I replaced the lights with a combination of Lutron RA2 and Caseta (old switches). I installed Zigbee motions throughout the house including several in the basement. I replaced the heated floor thermostats with Sinope TH1300ZB thermostats.
I programmed the floor to only turn on when someone was in the basement (via the zigbee motions) , the time of year can not be between June 15 - September 15, the AC can not be on cool and the AC can not be cooling. All must be true.
For lighting we had the outside lights programmed for Sunset and Sunrise. I programmed the lighting to turn off and the AC units to move up their thermostat (Ecobee) just by a few degrees when Armed Away (Ring Alarm; third party integration with Hubitat).
After the above changes the first bill with the majority from August (HOT) was $317. Now that is a good reason to automate.
You might want to check out those Aqara FP1's - they can detect the presence of people sitting/standing still. I've been testing in my powder room and it's been working great. I have a unit in my basement but haven't done anything with it yet.
Yeah I hear you.. these are supposedly Zigbee 3 and they are powered. I have 80+ devices in my ZB mesh and have not seen any dropoffs or other bad mesh behavior. I have 2 FP1s in operation. I believe others like @NoWon have more. They did mention that the FP1s might drop off after 12 hours or so and not auto-rejoin if powered off for that long.
Just to correct my original post that was linked.
I did more testing the FP1's auto rejoin works (mostly) fine unless they are knocked off the network from electronic interference caused by other devices.