Using wi-fi to see through walls

[Oric]

http://www.extremetech.com/extreme/133936-using-wifi-to-see-through-walls

[Samen]

That is an interesting one Oric.
I remember reading about it a while back, within the last year anyway.

Cell phone signals and how they bounce of targets can also be used for this, read about it some 6 years ago, it was a land based application where a bunch of cell phone towers were interconnected and through this passive "radar" system air space was being monitored in stealth mode.

Now they seem to be using satellites to use this system to track stealth planes.
http://www.popsci.com/military-aviation-space/article/2001-12/stealth-threat
http://www.geekosystem.com/reports-of-stealths-death-are-greatly-exaggerated/

UK military is detecting and identifying trucks from tanks and maybe even aircraft type by using this system.
http://www.businessweek.com/stories/2003-10-19/super-radar-done-dirt-cheap
http://www.newscientist.com/article/dn4299-cellphone-radar-tracks-traffic-flow.html

Maybe someone here can design the ultimate preppers 5 mile range cell phone based drone detector interconnected to the WiFi part to detect how many persons are in the black wan approaching ones dwelling down the street. Get that hooked up to a social network system and have good coverage of the "trust me I am with the government" types.