You're probably familiar with any number of ad hoc experiments where some journalist, law-enforcement officer or random clown successfully smuggles a gun or knife onto a plane, demonstrating the weakness of airport security.
These sorts of anecdotes make powerful memes, but what does the scientific evidence say about airport security?
According to a recent study by the Harvard School of Public Health, there's no evidence that X-raying carry-on luggage, taking off shoes and confiscating small items has prevented any hijackings or attacks.
The TSA defended the searches, claiming that they confiscated 13 million prohibited items in one year, "most" of which were cigarette lighters.
Bruce Schneier responded:
This is where the TSA has it completely backwards. The goal isn't to confiscate prohibited items. The goal is to prevent terrorism on airplanes. When the TSA confiscates millions of lighters from innocent people, that's a security failure. The TSA is reacting to non-threats. The TSA is reacting to false alarms. Now you can argue that this level of failures is necessary to make people safer, but it's certainly not evidence that people are safer.
The report in the British Medical Journal points out that widespread screening for threats to public health are usually only enacted if there is clear evidence that they work -- otherwise they do nothing to improve health and safety, but merely waste a lot of time and money for no gain:
With $6.5 billion spent globally on airport protection each year, the public should be encouraged to query some screening requirements – such as forcing passengers to remove their shoes, the researchers said.
"Can you hide anything in your shoes that you cannot hide in your underwear?" they asked.