Yes, you won't be able to do this on normal wifi traffic typically either, you need to send specific packets at a high enough rate (in between normal internet traffic) in order to sense with any accuracy, as I also remarked earlier: https://news.ycombinator.com/item?id=46976849
Yea, that makes sense as you would need quite a bit of information across a reasonable temporal range if the identifying qualities are movement related. Very interesting.
There'll be an update where a first responder can send a special packet to an SSID that will enable these high rate packets without needing to join the wifi. It'll be secure where only the good guys will know about it so that it won't be able to be used nefariously. /s
