Initially I am interested in room assistant also, but then I put that project on hold due to prices of the Pi Zero W.
At the moment I am following these 2 threads, thinking maybe they will stabilized soon in terms of compatibility, functions, etc.:
mmWave human presence for under $20?! - Hardware - Home Assistant Community (home-assistant.io)
New Aqara Human Presence Sensor FP1 - Hardware - Home Assistant Community (home-assistant.io)
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