Obviously this privacy violation equipment is immoral and will foster criminal activity rather than regulatory since regulation has been defunded.

there was a strikingly similar idea in an episode of Continuum.

How close does the RF source have to be? If there's no convenient access point, would a remote source through a high gain antenna work?
How well does it work with more than one moving body?

@alfie, passive radar has been used with some success for many years, it's just the same as ordinary radar except the signal is much much weaker, usually substantial computational resources are needed to make sense of the signal but it can be done: http://en.wikiped...ve_radar

Reminds me of the scene in Battleship where they used buoys that detect ocean displacement to track the aliens who were invisible to radar.

Are there any possibilities to direct this sort of "radar" downward using, say, microwave or such detection in order to "look" underground? Shallow for artifacts, deeper for minerals, for instance?

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Did Christopher Nolan research this subject to fictionalize the concept of using everyone's cellphone in Gotham City as passive radars? If he did, wow, that was some damn good research.