Check out this little trick: Wi-Spy - Hackster.io
Seems like we could put this in 2 or 3 ESP devices peppered around the home (rather than flying a drone around) and use it to detect what rooms people are in on the “cheap”.
I doubt you could get any real numbers about human beings like this. Other than “detecting” people this solution rather just could detect wifi enabled devices. And even if I carry a mobile phone around you still won’t be able to “detect” me as my wifi & bluetooth is off when I’m wandering around as I don’t want to be tracked 
Another fact to consider is that battery powered devices might not even affected by the used loophole called “Polite WiFi". The origin of this loophole (they don’t call it bug as it kind of works like intended) is the “feature” to easily onboard (new) devices (like smart sockets and stuff) to your local wifi. It is probably even limited to mains powered devices in the end… 
not 