A short history of airport security: We screen for guns and bombs, so the terrorists use box cutters. We confiscate box cutters and corkscrews, so they put explosives in their sneakers. We screen footwear, so they try to use liquids. We confiscate liquids, so they put PETN bombs in their underwear. We roll out full-body scanners, even though they wouldn’t have caught the Underwear Bomber, so they put a bomb in a printer cartridge. We ban printer cartridges over 16 ounces—the level of magical thinking here is amazing—and they’re going to do something else.

Take all the money spent on new security measures and spend it on investigation and intelligence. This is a stupid game, and we should stop playing it.

It’s not even a fair game. It’s not that the terrorist picks an attack and we pick a defense, and we see who wins. It’s that we pick a defense, and then the terrorists look at our defense and pick an attack designed to get around it. Our security measures only work if we happen to guess the plot correctly. If we get it wrong, we’ve wasted our money. This isn’t security; it’s security theater.

Bruce Schneier, “A Waste of Money and Time”