I believe Irving posted this story last year: http://www.radiolab.org/story/eye-sky/
The technology exists. We as a society have to decide whether catching criminals/terrorists is worth the ever present eye of government. IMO, this is an ethical question to be made by a society with a decreasing value on ethics.
Where and when do we have a reasonable expectation of privacy? I certainly expect that anything I do outside of my home is observable by any number of people and technologies scattered in both public and private locations. This particular technology does not prevent a crime but may assist in locating those who did commit a crime, which may in turn prevent future crimes that could be committed by those same people. The story points out a critical weakness in our current system of intelligence gathering; we do not have enough analysts to analyze the data in a timely fashion. Why have an alarm if no one is available to respond when it goes off?