[SEJeff]

And in specific, lookup Tomographic Motion Detection ala:

https://www.youtube.com/watch?v=Y8updJWoSxE

http://www.securityelectronicsandnetworks.com/articles/2014/...

[captn3m0]

This is a nice piece of recent research: Keystroke Recognition Using WiFi Signals

[0]: https://www.sigmobile.org/mobicom/2015/papers/p90-aliA.pdf