I’m curious as to how feasible it would be to get signal strength from my router’s client list as either a sensor or device tracker attribute. The DD-WRT dashboard shows the signal strength in the wireless client list - when I move my phone from my office to my living room the signal drops from about -40 to -55. The Wiviz site scan feature even plots the relative location of devices in a 3D graphic (beamforming / directional features may be required for this).
While it may not be reliable enough to be the single source of truth for room-based presence detection (then again, I do have multiple routers…), it could overcome the constant struggle with phones dropping and rejoining the network while in sleep mode. Simply look at the signal strength trend - if it hits a certain downward threshold, confirm the device as away, otherwise check again in a few minutes.