Wi-Fi fills our world with radio waves. In your home, in the office, and increasingly on city streets, humans are bathed in a constant background field of 2.4- and 5-gigahertz radio signals. And when people move, they distort this field, reflecting and refracting the waves as they go.
But all these systems have drawbacks. For example, they rely on knowing the exact position of the Wi-Fi transmitters involved and need to be logged in to the network so that they can send known signals back and forth.
That isn’t possible for the ordinary snooper or peeping tom, who might typically have access only to off-the-shelf Wi-Fi sniffers such as those built into smartphones. This kind of set-up is just too basic to reveal any useful detail about what goes on behind closed doors, other than the presence of the Wi-Fi network itself.
At least, that’s what everybody thought. Today that changes thanks to the work of Yanzi Zhu at the University of California, Santa Barbara, and colleagues. These guys have found a way to see through walls using ambient Wi-Fi signals and an ordinary smartphone.
They say the new technique allows an unprecedented invasion of privacy. “Bad actors using smartphones can localize and track individuals in their home or office from outside walls, by leveraging reflections of ambient Wi-Fi transmissions,” they say.
First some background. If humans were able to see the world as Wi-Fi does, it would seem a bizarre landscape. Doors and walls would be almost transparent, and almost every house and office would be illuminated from within by a bright light bulb—a Wi-Fi transmitter.
But despite the widespread transparency, this world would be hard to make sense of. That’s because walls, doors, furniture, and so on all reflect and bend this light as well as transmitting it. So any image would be impossibly smeared with confusing reflections.
But this needn’t be an issue if all you are interested in is the movement of people. Humans also reflect and distort this Wi-Fi light. The distortion, and the way it moves, would be clearly visible through Wi-Fi eyes, even though the other details would be smeared. This crazy Wi-Fi vision would clearly reveal whether anybody was behind a wall and, if so, whether the person was moving.
That’s the basis of Zhu and co’s Wi-Fi-based peeping tom. It looks for changes in an ordinary Wi-Fi signal that reveal the presence of humans.
Read more at Source; MIT Technology Review