By CBSLA Staff

LOS ANGELES (CBSLA) – In the 20 years since the 9/11 terrorists attacks, both national and domestic security measures have changed dramatically, most notably at the country’s airports.

“Regarding the question of how security has changed since 9/11, there really is only one answer and that is everything,” said security expert Jeffrey Simon, an author and visiting lecturer at the University of California, Los Angeles’ Department of Political Science. “Basically, security now after 9/11 is every part of our everyday lives. Wherever we go, whether it be concerts, movie theaters, sporting events…”

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According to Simon, 9/11 transformed the way the government and law enforcement protect residents every single day since, as well as the way the country is willing to be protected, from how people are monitored in public places to intelligence gathering and the war on terrorism.

He said it’s a never ending technological race against those who want to harm the country.

There are now more than 50,000 TSA agents working in commercial airports nationwide.

“Ultimately, every device we come up with, terrorists are going to try to think of a way of penetrating it,” Simon said.

Airport and airplane security have undergone the most noticeable changes when it comes to security measures after the 9/11 attacks.

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“The days of being able, you know, to wave at people as they pulled away at the gate at the window, those days are long gone,” said the former director of security at the Denver airport, Jeff Price. There were 33 air marshals on duty during 9/11, and by on duty, I don’t mean they were working that day. I mean, there was 33 air marshals that were employed by the entire FAA.”

There are now thousands of air marshals, along with more than 50,000 agents of the Transportation Security Administration, a department created just weeks after 9/11.

“They had two employees the day they were created. They were given the mandate to take over all screening at commercial service airports within a year,” Price said.

Both Simon and Price agree that there’s no doubt that the change have likely thwarted another major attack, but also agree it only takes one day for everything to change again.

“No matter how many times we are protected against terrorism and security works, the terrorists only have to penetrate the system once to make it seem like we’re going back to square one,” said Simon.

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For all the security that people see, experts say there’s much more work going on behind the scenes to keep people safe.