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WiFi routers can see people through walls
(www.zmescience.com)
This is a most excellent place for technology news and articles.
I could see this deployed in hotels or other public places by the CIA so they can monitor their target's movements. The main benefit is it doesn't require placing a bug in the room because the routers could be placed in another room, so if the room is swept for bugs, they won't find anything suspicious. Not too far-fetched considering the kind of shenanigans they frequently do aboard.