Caleb Harmon-Marshall was a Transportation Security Administration agent for about eight years and spent most of that period at the world's busiest airport, Hartsfield-Jackson Atlanta International Airport.

He told Business Insider to be vigilant while waiting for security checks. He said this area isn't secure, meaning anyone can walk in off the street carrying weapons.

"I would never wear headphones prior to going through security," he said. "You want to be very mindful of what's going on in your surroundings."

He said that once you're through TSA, you can zone out as much as you want. But before and during the screening, you should be listening for announcements.

"The key is to listen to that first officer that you see past the ID check; they're going to tell you what to do," he said.

"I know we tune them out because we're so focused on: 'I need to make sure I'm doing everything; I don't want to get yelled at.' But really take a moment. Just stop, listen to what that officer is saying, and then proceed."

Making sure you're alert can make the whole process easier. Harmon-Marshall said the security is always different as a safety measure to ensure it's not predictable. But there are certain things you can look out for.

"If you see a K-9, nine times out of 10, you'll probably be able to keep your shoes on, because they're doing risk-based screening at that moment," he said. "If you don't see a K-9, you're most likely going to have to take off your shoes, take your laptop out of your bag, all those things that they tell you to do."

You should also stay alert on the plane, especially if you sit in one of the emergency-exit rows.

Harmon-Marshall said some travel influencers say sitting here is a hack to get more legroom, but people should know what they're signing up for.

"Many people, they sit in those seats and they don't know that they are subject to helping when an emergency actually happens," he said. "And if they fail to help, they can potentially face federal charges."

He said people should be aware of what they need to do in the case of an emergency, rather than agree to help without thinking about the consequences.

People don't think an emergency will happen and so just say "yes" when they're asked if they will help.

"If you're saying 'yes,' make sure that you are really committed to helping the flight attendant when that happens," Harmon-Marshall said.

On the plane, you also shouldn't stand up whenever you want, Harmon-Marshall said, because turbulence can hit at any time. A freak incident could also occur, such as when a hole ripped open in the plane's fuselage on a recent Alaska Airlines flight and sucked out passengers' belongings.

"You should probably be seated as much as possible and wearing your seat belts," Harmon-Marshall said.

Pilots will often warn when turbulence is ahead, but they "don't see everything," he said.

"There are clear pockets where they're not aware that they're about to hit and they can be very severe," he said.

Harmon-Marshall became a travel influencer during the pandemic, and his TikTok account, where he posts tips about air travel, has grown to more than 150,000 followers.

He also runs the newsletter Gate Access, which provides more in-depth advice, such as how to properly use overhead bins and which airlines have "customers-of-size" policies.