Several years back we actually made use of the principle mentioned in this post, to more systematically count traffic on the roads [1]. In our case we used LTE/4G radio, and we could even estimate the direction of travel, as well as the type of traffic (pedestrian, small vehicles, large vehicles). It was more accurate than Google Maps because it was independent of the moving phone, i.e. it was "sensing the obstacles in the environment".

[1] "Traffic Flow Estimation using LTE Radio Frequency Counters and Machine Learning", https://arxiv.org/abs/2101.09143

Now, about the wifi part, why isn't there an Home Assistant extension that detects already room presence magically exploiting all of this??

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