Interference and crosstalk: Both 24GHz and 60FHz mods are tolerant of other emitters in their field of view, so you could pair two of them in the outside corner of your ell, looking towards the ends and a third at the long end of the ell looking back towards the corner and they ought not to interfere. Another possible configuration would be three ceiling mounted emitters looking down, overlapping the fields of view for full coverage of the floor area. A 60° field of view at 2.8m gives you roughly a 5m radius of detection on the floor.

Seeing through walls: "Thin walls" attenuate the signal, but allow enough penetration to detect people through cover. The radar can penetrate thin plastic housings, plexiglass, cloth, drywall, wood paneling, and thin plaster & lath. It cannot penetrate glass, stone, or metal. Same goes for floors. My radar module will detect people in the unfinished room below my home office through the hardwood floor if I angle it down far enough.

Fast detection: I found that while the radar was responsive even to small movement nearly instantly, it takes up to 2 or 3 seconds to acquire and classify a target as a person. Once t locks on, it pretty reliably tracks the person for as long as they are in view. In practice, a person walking into the edge of the field of view at a normal walking pace could cover half the field before they are detected as present. It "feels" a bit slow compared to PIR detection which is sub-second in most cases, but generates a lot of false positives. The technique I am refining is to position the the radar to detect a person entering a room by angling the radar field of view to "lead lead target" and use the PIR to determine the target has moved into a zone where I want action to take place. In essence, I want the lights to trip on when the radar detects human presence AND the PIR sees a hot blob. Then I kick on the light and wait for the human presence detection to go back to unoccupied for 5 minutes before turning off the light. I might also experiment to see if ultrasonic detection is any more reliable than IR, since it wouldn't be fooled by warm/cold draughts, or by sudden changes in light as from dappled shade or clouds & sun. My concern is I have pets and wouldn't want to stress them with sound I can't hear, but maybe they can. Need to research it more.

Its been fun playing with this stuff, but I might note that at this point you can just buy an open platform (as in open source) esphome/HA compatible multisensor presence detector made by the guy who does the Everything Smart Home channel on YouTube. He posted a couple videos talking about it (links below). For me, this is just messing around with something I always wanted to play with, but I'll probably just buy a kit when I want to hang something functional on a ceiling or wall.

Definitely check out the videos I linked. They're excellent for helping to understand the pros and cons of this tech in real-world smart home applications.

Everything Smart Home - Building my own smart ho e oresense sensor

• https://youtu.be/boWsjJlgzag
• https://youtu.be/wCwMNSeLRcw