[Delayed response: sorry.] On Thu, 1 Oct 2009, Eugen Leitl wrote: <snip>

Researchers at the University of Utah say that the way radio signals vary in a wireless network can reveal the movement of people behind closed doors. <snip>

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 is possible to build up a picture of the movement within it.

Isn't this the same premise behind over-the-horizon "passive radar" (yeah, Im pretty sure that's not the formal name for it - its just as close as I can remember)? It sure sounds like it, and if so, it's hardly new - just applied to a different target class. <snip>

The advantage of this technique over others is first its cost. The nodes in such a network are off the shelf and therefore cheap. Other through-wall viewing systems cost in excess of $100,000.

And more importantly, the likely oberservers won't be paying for the networks which will provide all of the wonderful passive imaging: the targets will set up their own imaging nets. //Alif -- "Never belong to any party, always oppose privileged classes and public plunderers, never lack sympathy with the poor, always remain devoted to the public welfare, never be satisfied with merely printing news, always be drastically independent, never be afraid to attack wrong, whether by predatory plutocracy or predatory poverty." Joseph Pulitzer, 1907 Speech