ATLANTA (AP) – A woman flying out of Philadelphia’s airport last year remembered to pack snacks, prescription medicine and a cellphone in her handbag. But what was more important was what she forgot to unpack: a loaded. 380-caliber handgun in a black holster.

The weapon was one of the 6,542 guns the Transportation Security Administration intercepted last year at airport checkpoints across the country. The number—roughly 18 per day—was an all-time high for guns intercepted at U.S. airports, and is sparking concern at a time when more Americans are armed.

“What we see in our checkpoints really reflects what we’re seeing in society, and in society there are more people carrying firearms nowadays,” TSA administrator David Pekoske said.

With the exception of pandemic-disrupted 2020, the number of weapons intercepted at airport checkpoints has climbed every year since 2010. Experts don’t think this is an epidemic of would-be hijackers—nearly everyone caught claims to have forgotten they had a gun with them—but they emphasize the danger even one gun can pose in the wrong hands on a plane or at a checkpoint.

Guns have been intercepted literally from Burbank, California, to Bangor, Maine. But it tends to happen more at bigger airports in areas with laws more friendly to carrying a gun, Mr. Pekoske said. The top 10 list for gun interceptions in 2022 includes Dallas, Austin and Houston in Texas; three airports in Florida; Nashville, Tennessee; Atlanta; Phoenix; and Denver.

Mr. Pekoske isn’t sure the “I forgot” excuse is always true or whether it’s a natural reaction to getting caught. Regardless, he said, it’s a problem that must stop.

When TSA staffers see what they believe to be a weapon on the X-ray machine, they usually stop the belt so the bag stays inside the machine and the passenger can’t get to it. Then they call in local police.

Repercussions vary depending on local and state laws. The person may be arrested and have the gun confiscated. But sometimes they’re allowed to give the gun to a companion not flying with them and continue on their way. Unloaded guns can also be placed in checked bags assuming they follow proper procedures. The woman in Philadelphia saw her gun confiscated and was slated to be fined.

Those federal fines are the TSA’s tool to punish those who bring a gun to a checkpoint. Last year TSA raised the maximum fine to $14,950 as a deterrent. Passengers also lose their PreCheck status—it allows them to bypass some types of screening—for five years. It used to be three years, but about a year ago the agency increased the time and changed the rules. Passengers may also miss their flight as well as lose their gun. If federal officials can prove the person intended to bring the gun past the checkpoint into what’s called the airport’s sterile area, it’s a federal offense.

Retired TSA official Keith Jeffries said gun interceptions can also slow other passengers in line.

“It’s disruptive no matter what,” Mr. Jeffries said. “It’s a dangerous, prohibited item and, let’s face it, you should know where your gun is at.”

Experts and officials say the rise in gun interceptions simply reflects that more Americans are carrying guns.

The National Shooting Sports Foundation, an industry trade group, tracks FBI data about background checks completed for a firearm sale. The numbers were a little over 7 million in 2000 and about 16.4 million last year. They went even higher during the coronavirus pandemic.

For the TSA officers searching for prohibited items, it can be jarring.

In Atlanta, Janecia Howard was monitoring the X-ray machine when she realized she was looking at a gun in a passenger’s laptop bag. She immediately flagged it as a “high-threat” item and police were notified.

Ms. Howard said it felt like her heart dropped, and she was worried the passenger might try to get the gun. It turns out the passenger was a very apologetic businessman who said he simply forgot. Ms. Howard says she understands travel can be stressful but that people have to take care when they’re getting ready for a flight.

“You have to be alert and pay attention,” she said. “It’s your property.”

Atlanta’s airport, one of the world’s busiest with roughly 85,000 people going through checkpoints on a busy day, had the most guns intercepted in 2022—448—but that number was actually lower than the year before. Robert Spinden, the TSA’s top official in Atlanta, says the agency and the airport made a big effort in 2021 to try to address the large number of guns being intercepted at checkpoints.

An incident in November 2021 reinforced the need for their efforts. A TSA officer noticed a suspected gun in a passenger’s bag. When the officer opened the suitcase the man reached for the gun, and it went off. People ran for the exits, and the airport was shut down for 2.5 hours, the airport’s general manager Balram Bheodari said during a congressional hearing last year.

Officials put in new signage to catch the attention of gun owners. A hologram over a checkpoint shows the image of a revolving blue gun with a red circle over the gun with a line through it. Numerous 70-inch television screens flash rotating messages that guns are not allowed.

“There’s signage all over the airport. There is announcements, holograms, TVs. There’s quite a bit of information that is sort of flashing before your eyes to just try to remind you as a last ditch effort that if you do own a firearm, do you know where it’s at?” Mr. Spinden said.

Miami’s airport also worked to get gunowners’ attention. The airport’s director told Congress last year that after setting a gun interception record in 2021 they installed high-visibility signage and worked with airlines to warn passengers. He said the number of firearms intercepted declined sharply.

Mr. Pekoske said signage is only part of the solution. Travelers face a barrage of signs or announcements already and don’t always pay attention. He also supports gradually raising penalties to grab people’s attention.

But Aidan Johnston, from the gun advocacy group Gun Owners of America, said he’d like to see the fines lessened, saying they’re not a deterrent. While he’d like to see more education for new gun owners, he also doesn’t think of this as a “major heinous crime.”

“These are not bad people that are in dire need of punishment,” he said. “These are people who made a mistake.”

Officials believe they’re catching the vast majority, but with 730 million passengers screened last year even a miniscule percentage getting through is a concern.

Last month, musician Cliff Waddell was traveling from Nashville, Tennessee, to Raleigh, North Carolina, when he was stopped at the checkpoint. A TSA officer had seen a gun in his bag. Waddell was so shocked he initially said it couldn’t be his because he’d just flown the day before with the same bag. It turned out the gun had been in his bag but missed at the screening. TSA acknowledged the miss, and Mr. Pekoske says they’re investigating.

When trying to figure out how the gun he keeps locked in his glove compartment got in his bookbag, Mr. Waddell realized he’d taken it out when he took the vehicle in for repairs. Mr. Waddell said he recognizes it’s his responsibility to know where his firearm is but worries about how TSA could have missed something so significant.

“That was a shock to me,” he said.