I doubt anyone honestly thinks that DHS, DARPA and other such groups are using the same technology that you can buy at your tradeshows, but this article from the New Scientist online magazine shows just where DHS is pushing in technology.
Called the FAST program (Future Attribute Screening Technologies), this concept is a sensor array designed to find people who might be planning an attack or crimes. Yes, it certainly does sound a bit like the whole "pre-crime" concept out of the Minority Report movie. From the little we know, it sounds like such a system could study heart rates, facial expressions, breathing rates, etc.
While it seems that most citizens reading about this technology are alarmed by it, I think that it's not that much different than what security professionals already look for in places like airport security queues. Especially nervous, fidgety persons who keep muttering under their breath "death to America" are likely to be pulled out of line for further questioning and more in-depth screening.
The way I see this system is that it's just an automated, robot-like version of what we as humans do all the time. I believe we, as humans, are constantly studying expressions and attributes of others. If you are walking through the city back to your car at 11 p.m. and you see a mean-looking guy dressed in a hoodie hanging out in an alley, I'll venture to bet that you will avoid that alley and go around the block to reach your car. In essence, you've done a complex analysis of trying to guess what some person's intentions were. That, it seems is all this system does. You're not assuming the man must be a criminal just because of how he looks. Right or wrong, what you're doing is saying that his profile/appearance matches your experience with criminal appearances.
In the same way, part of the reason that terrorist Ahmed Ressam was caught before he could attack the Los Angeles airport is that a U.S. Customs inspector noted how nervous he was. Here's how nervous Ressam was: When asked to show ID he reportedly handed over a retailer's club membership card.
Here's what the New York Times wrote about this case:
"The inspector, Diana Dean, now retired, said later that she sensed Mr. Ressam was extremely nervous and that the convoluted route he described taking from Canada to the city he called "Sattle" made no sense to her." [see full NYT article]
This was admittedly a very long post for a short article, but as we push forward into advanced technologies beyond motion sensors, fire detectors and simple camera-recorder systems, we are obviously going to start facing more and more ethical and privacy-related issues. But keep in mind that such technological feats are only designed to automate what we are already doing to protect our nation's security.