A paper on breath and heartrate monitoring through walls by "illuminating"
human subjects with microwaves and processing the backscattered waves:
http://search.dis.anl.gov/plweb-cgi/mhrexpage.pl?0707732+1+5+_free_user_+1%2bminute+60+0+unix+1416+table+mhrex-user+query+doe%3adod%3ahhs%3acia%3ava%3a+microwave
This is at the DOE openness site on human radiation experiments:
http://tis.eh.doe.gov/ohre/
Search there on "microwave" or perhaps "heart" if the above url is too long.
The Washington Post reported a year or so ago that a company was
looking to market a device that could locate humans by remotely and passively
detecting the ELF electromagnetic waves put out by the beating of a heart.
Check one of the online patent pages, like the IBM patent site.
There are several patents for remote heartbeat detection, among other
remote biosensing devices:
http://patent.womplex.ibm.com/home
Promising technology with serious abuse potential in unscrupulous hands (of
which there never seems to be any shortage).
--
Allen L. Barker
http://www.cs.virginia.edu/~alb
