Not even a password protects you. Most of us spend our lives inside areas with Wi-Fi signals. But what we didn’t know until recently is that wireless routers can literally “see” us. When people move through the signal, even if they’re not in the same room as a router, their bodies disrupt waves in patterns that allow observers with special software to identify individuals and even read lips. As this “vision” comes into wide use, private lives — even without wayward webcams — could become a quaint concept.