Last week's deadly suicide bombing in the arrivals terminal at Russia's largest airport in Moscow raised inevitable questions about the vulnerability of public areas outside airports' secure spaces.
No major changes were immediately made to U.S. security policies following the explosion at Moscow's Domodedovo Airport that killed 35 people and injured 76. But the Transportation Security Administration last week said that "passengers may continue to notice unpredictable security measures in all areas of U.S. airports, including before the checkpoint.
"These measures include explosive detection technology, canine teams and Visible Intermodal Prevention and Response teams, among other measures both seen and unseen."
Christopher Bidwell, vice president of security and facilitation at the Airports Council International, North America, said that just because travelers don't see a security presence doesn't mean it isn't there.
"With regard to security at airports in the U.S., we have a multilayered security system that involves things that go on behind the scenes that might not be visible to the traveling public, and this includes security in public areas," he said.
He added that intelligence that emerges from the details of the suicide bombing could lead to changes or enhancements to the current security strategy.
Immediately following the attack, Russian authorities ordered security screenings of all people entering the country's airports as well as screenings of their baggage, state news agency Ria Novosti reported.
But according to Douglas Laird, a former secret service agent and president of Laird & Associates, an aviation security consulting firm, security can be increased only so much.
"Nothing is 100%," said Laird. "Let's say that we double the presence of uniformed police officer at airports. To me, that in and of itself lets the terrorists gain a couple of notches on their scale, and it shows we're terrified. I call it 'security theater.' "
Laird said that intelligence and security measures that prevent an attacker from reaching the airport are more important than what goes on inside the terminal.
"If you're looking at terrorism, by the time the person gets to the airport, or the train station, you've pretty much lost the battle," said Laird.
Part of the problem with large, public transportation hubs like airports, Laird said, is that "you inherit the infrastructure that you have ... If you were to build an airport from scratch, you would have a lot of options."
For instance, he said, if a checkpoint were established for cars driving into large airports such as Los Angeles Airport or Chicago's O'Hare, it would create a dangerous and time-consuming backlog of vehicles.
Instead, Laird said, one of the most effective security techniques on the ground is to have people with extensive training on the lookout for "unusual behavior."
"I liken it to being a lifeguard," said Laird. "You can watch literally hundreds of people, but what stands out is people that are in trouble."