Scientists in Germany have demonstrated a startling new form of surveillance: identifying people using nothing more than ordinary WiFi signals. By analyzing how radio waves bounce around a room, researchers can effectively “see” and recognize individuals — even if they are not carrying a device and even if their phone is turned off.
The statement from the article was the unlike previously, they used current consumer equipment, and could uniquely identify a specific person. I believe previous versions could just identify that there was “A” person. I don’t know that all that is true, but it is what the article says, and my vague memories line up.