Nearly 40 million passengers travel through SFO each year.
From long lines to body scans to mini carry-on size liquids, the sweeping changes in airport security post 9-11 have become a way of life for people here in the Bay Area and across the country.
And it's not over. Aviation security is in a constant state of evolution, said Erroll Southers, now Associate Director of the Homeland Security Center at University of Southern California.
In the days following the terrorist attacks on September 11, 2001, what suddenly was being called "Homeland Security" became a national priority, with its own cabinet-level department.
Under Homeland Security, Congress created the Transportation Safety Administration, the TSA, to take control of aviation security from a patchwork of private security firms at 450 airports.
As part of the largest reorganization of the government since that undertaken by the Truman Administration after World War II, the TSA hired, trained, and equiped 50,000 federal screeners.
Since then, techniques and technology have undergone perpetual evolution.
"Implement, evaluate, adjust," is the process, according to Nico Melendez, a TSA spokesman in Los Angeles.
In the decade since 9-11, TSA has helped keep the skies remarkably free of terrorism, though there certainly have been continued attempts.
Overseas, there have been a number of alarming security breaches.
Fortunately, the plots did not achieve their objectives. Nevertheless, the breaches led TSA to respond with counter measures:
*Since inept "shoebomber" Richard Reid was foiled late in 2001, air travelers have had to remove their shoes for screening.
*Since the British thwarted a plot involving liquid explosive in 2006, there have been limits on carrying aboard fluids.
*Since the Nigerian Umar Farouk Abdulmutallab suffered burns to his crotch in-flight on Christmas Day, 2009, authorities have sought ways to prevent anyone else from hiding explosives in their underwear. That led to a new generation of machines to perform full body scans, or in the alternative, flyers could choose to undergo "enhanced" pat downs.
Not all travelers have welcomed the intensified security.
"I think we're going a little overboard," said traveler Kevin Green, after checking in for a flight from LAX to Austin, TX.
"It is a hassle," said Diana Rodriguez, taking her two young children through Terminal One.
Southers acknowledged the truth of those perceptions.
"Unfortunately, we've done a pretty good job of making air travel an unpleasant experience," he said.
A groundswell of resentment against scanners that virtually see through clothing, and enhanced pat downs that bring unwanted intimacy, found voice last fall with one San Diego traveler's memorable response, "Don't touch my junk!" It went viral and became a catchphrase.
"We're beginning to see pushback, where people are almost becoming adversaries of the security systems that are put in place to protect them.," said Brian Jenkins, an anti-terrorism expert.
"Now that's a good way to destroy a security system, and we have to address that as an issue," said Jenkins, co-editor of "The Long Shadow of 911: America's response to Terrorism," published by the Rand Corporation think tank.
But at the same time Americans resist more invasive security, Jenkins said, they also expect the government to respond forcefully -- and at great expense-- to any terrorist threat.
Case in point, he said, is Abdulmutallab, the young Nigerian with the bomb in his underpants. The bomb didn't work, but the reaction of the country was extraordinary,
"We are throwing down a billion dollars to deploy body scanners at airports across the country," he said. The terrorists "invested a few thousand. We throw down a billion."
In terms of the American resources expended, this failed effort at terrorism was, in reality, "a huge terrorist success," Jenkins said
Jenkins worries that current approach -- responding to each terrorism attempt with a massive new security crackdown -- is unsustainable and probably ineffective.
"The long term problem there is that terrorists can build small devices, small explosive devices, and conceal them in ways that make them undetectable to anything but the most intrusive inspections," he said "We're going to lose that battle in the long run."
The answer, Jenkins and a growing chorus of experts agree, is increased focus on risk-based security to maximize effectiveness.
"We really are in the risk management business," said USC's Southers, a law enforcenent veteran, anti terrorism authority, and one-time nominee for TSA Director.
In fact, maximizing effectiveness is a focus of USC's Homeland Security Center, which is officially called the National Center for Risk and Economic Analysis of Terrorism Events.
"No matter how much we spend, you know, no matter how much we do, we may still be victim of an atttack in the future. However, we do believe we can spend more wisely. We understand where those risks and threats are," said Southers, who sees TSA adapting. "They're getting closer. They've at least shifted from being object-centric and device-centic to understanding that the human element is really what's important."
One inevitable concequence is a less egalitarian approach to security. "After doing this for 10 years, we do know that not every passenger poses the same level of threat," said Nico Melendez, TSA spokesman in Los Angeles.
A "Trusted Traveler" pilot program being launched this fall would provide a streamlined screening process for frequent flyers who have undergone a background check. Initially, this will be available only with Delta Airlines in Atlanta and Detroit, and American Airlines at Miami and Dallas.
The resources not expended on "trusted" travelers could be allocated to more detailed focus on other passengers, selected both at random and through behavioral analysis.
"By re-allocating these resources, and then rigorously testing this, we can really begin to get some efficiencies that will in fact increase our effectiveness," said Jenkins. "We won't have the Israeli model of come to the airport three hours in advance and be interrogated. But we'll have some components, the best components, of a number of different approaches."
Traveler Green voiced hope that someday the terror threat will recede and America will be able to relax the levels of security. "At some point, I hope we can scale back," Green wishes.
But is that a realistic expectation?
"Terrorism will not go away, and the threat is not going to go away. We can reduce it and we're doing a better job of that. I think the system is working much better. But aviation is always going to be near the top of the list in terms of high-utility targets for terrorists," said Southers.
"I don't think we're looking at perpetual war," said Jenkins. "But we're probably, realistically, looking at perpetual preparedness.
"Now how we deal with that in an open, democratic society--and remain a democratic society--is one of the challenges that we face going forward."