> "By observing the propagation of radio waves, we can create an image of the surroundings and of persons who are present,"

Notice that it doesn't matter if you are using Wifi. If you're in a city, I doubt there are many places that lack Wifi radio waves.

Thank you to the researchers (seriously) for revealing this to the public rather than selling it to the highest bidder. Though I suspect that, given how obvious it is once you think about it - all these radio waves solve many problems of passive imaging - it's already known to some people.