See Through Walls With Wireless Networks See through walls by
using the way signal strength varies in wireless networks? It
ought to be possible and now researchers at the University of
Utah say that they can do it with variance-based radio
tomographic imaging (VRTI). According to their paper, VRTI
images movement, not static changes in attenuation. In the image
below, a human subject is taking small steps randomly around and
through the space marked as (17.6, 21.3) in the graph shown
below. The white spot shows where VRTI 'sees' the subject.
(Wireless network spying with variance-based radio tomographic
imaging ) The basic idea is straightforward. The signal strength
at any point in a network is the sum of all the paths the radio
waves can take to get to the receiver. Any change in the volume
of space through which the signals pass, for example caused by
the movement of a person, makes the signal strength vary. So by
"interrogating" this volume of space with many signals, picked
up by multiple receivers, it