Wireless devices are everywhere, at home, at the office, and on the street. Devices are bombarding us with transmissions across a wide range of RF frequencies. Many of these invisible transmissions reflect off our bodies, carrying off information about ou location, movement, and other physiological properties. While a boon to professionals with carefully calibrated instruments, they may also be revealing private data about us to potential attackers nearby.
In this paper, we examine the problem of adversarial WiFi sensing, and consider whether ambient WiFi signals around us pose real risks to our personal privacy. We identify a passive adversarial sensing attack, where bad actors using a single smartphone can silently localize and track individuals in their home or office from outside walls, by just listening to ambient WiFi signals. We experimentally validate this attack in 11 real-world locations, and show user tracking with high accuracy. Finally, we propose and evaluate defenses including geo-fencing, rate limiting, and signal obfuscation by WiFi access points.