The lights are dimmed in the Security Operations Center at San Francisco International Airport, where Kathryn Knoblauch watches a dozen monitors fed by the 1,500 surveillance cameras scattered through this busy and sensitive facility.

At the far right of her field of view sits the newest tool in the airport's security toolkit -- and the latest worry for civil libertarians. It's a computer monitor that displays images, selected by a new type of software, that sifts through that stream of surveillance video, sending out alerts when it detects certain actions or situations.