Taking off your shoes at the airport. Bloated no-fly lists. Random screenings and searches. Little plastic bags full of 3-ounce liquid containers. All of these measures were reactionary responses to terrorism on airlines. None of it works.

All of this, however, is the definition of security theater:

Security theater consists of security countermeasures intended to provide the feeling of improved security while doing little or nothing to actually improve security. The term was coined by Bruce Schneier for his book Beyond Fear, but has gained currency in security circles, particularly for describing airport security measures. It is also used by some experts such as Edward Felten to describe the airport security repercussions due to the September 11 attacks. Security theater gains importance both by satisfying and exploiting the gap between perceived risk and actual risk.

Taking off your shoes at the airport does nothing to prevent terrorist attacks on airlines. The shoe-bomber plot was foiled, and that particular technique is unlikely to be tried again. Instead, we’ll get new methods, like the most recent over Christmas in Detroit, with condoms full of explosives taped to legs.

What’s next in this game of whack-a-mole? We’re already hearing of new restrictions aimed at thwarting this latest incident, which is unlikely to be repeated:

According to a statement posted Saturday morning on Air Canada’s Web site, the Transportation Security Administration will severely limit the behavior of both passengers and crew during flights in United States airspace — restricting movement in the final hour of flight. Late Saturday morning, the T.S.A. had not yet included this new information on its own Web site.

"Among other things," the statement in Air Canada’s Web site read, "during the final hour of flight customers must remain seated, will not be allowed to access carry-on baggage, or have personal belongings or other items on their laps."

What’s next, flying without pants? How about the logical extreme, flying naked?

Republicans (and Joe Lieberman) are already up in arms about how the "system" didn’t work and how we’ve got to launch another invasion. Of course the system didn’t work! It’s not designed to work. The airline security system is designed to give scared Americans a feeling of security, right down to National Guard troops in airports with huge machine guns that contain no bullets. Meanwhile, as Schneier and others point out, security theater has real costs. The screening technology at airports cost money. The embarrassing screening procedures take time. Garbage-in, garbage-out no-fly lists erode our civil liberties and privacy. And, as Laura Clawson points out, none of this has done anything to reduce terrorism on airlines:

In the wake of 9/11, Malcolm Gladwell wrote a New Yorker article on the history of hijackings (PDF), concluding:

Can we close the loopholes that led to the September 11th attack? Logistically, an all-encompassing security system is probably impossible. A new safety protocol that adds thirty seconds to the check-in time of every passenger would add more than three hours to the preparation time for a 747, assuming that there are no additional checkpoints. Reforms that further encumber the country’s already overstressed air-traffic system are hardly reforms; they are self-inflicted wounds.

The history Gladwell had detailed is one in which, repeatedly, security procedures on air travel had addressed the most recent crime or attempted crime, always looking backward and always being evaded by the next round of hijackers.

And, despite all the improvements in airport security, the percentage of terrorist hijackings foiled by airport security in the years between 1987 and 1996 was at its lowest point in thirty years. Airport-security measures have simply chased out the amateurs and left the clever and the audacious. "A look at the history of attacks on commercial aviation reveals that new terrorist methods of attack have virtually never been foreseen by security authorities," the Israeli terrorism expert Ariel Merari writes, in the recent book "Aviation Terrorism and Security."

So what can be done to actually make us safe, as opposed to waste our money and our time and make us feel safe? Well, we can start looking at the hard questions. Why do people who live across the world want to kill innocent Americans? What makes these people so violent? What policies have we pursued across the world to get so many people so angry with us?

There will always be crazy people, and the world will never be perfectly safe. But we get more terrorism when we do things as a nation and as a society that cause these crazy people to organize with each other, and give them the climate to work with the moneyed backers and political leaders who would never give them the time of day otherwise. The term is blowback, and it’s well-defined and real.

If we can take away the causes that create sympathy for terrorism and turn terrorists into martyrs around the world, then we will cut actual terrorist incidents to almost nothing. But if we don’t, all we’ll have to rely on is security theater.