Identification. Not with Al Qaeda or the Unabomber. All it takes is a means of identification, like a driver's license. I have been riding Amtrak lately and visiting with editors in various high rises, and everywhere I go I am asked for a photo ID. Like most people, I show my license. I guess non-driving terrorists might momentarily be thwarted by this measure, but it's hard to imagine what else is accomplished aside from slowing down normal comings and goings.
I am reminded by these episodes of Bruce Schneier's comment about "security theater." While it's true that security used to be absurdly lax--I was once served with a subpoena in the middle of the LA Times newsroom--I have to wonder if we are doing much good now with all the passes and other measures employed in Manhattan office towers. I suppose if nothing else we are giving comfort to the lawyers.