Use WiFI to See Behind Walls

An expected privacy ploy.  More presence rather than details?

Using Wi-Fi to 'See' Behind Closed Doors Is Easier than Anyone Thought 
Technology Review

University of California, Santa Barbara researchers have developed a technique to see through walls using ambient Wi-Fi signals and an ordinary smartphone. The team said the new method allows for an unprecedented invasion of privacy, as bad actors using smartphones can localize and track individuals in their homes or offices from outside by leveraging reflections of ambient Wi-Fi transmissions. The system looks for changes in an ordinary Wi-Fi signal that reveal the presence of humans, which can be detected by walking near a room or building several times. The researchers said that "with more than 2 Wi-Fi devices in a regular room, our attack can detect more than 99% of the user presence and movement in each room we have tested."   ... '