More sophisticated cameras. Security robots. Customers feeling shaken by recent attacks at U.S. malls may not notice huge changes — but mall operators are testing and putting in place new technologies and other measures to offer people more protection without intruding too much on their shopping time.

Mall executives say shoppers have been adamantly opposed to airport security tactics like metal detectors. So they're trying other things, and increasingly using mass notifications that let them send text and email alerts to tenants within seconds in case of a crisis.

Concerns about safety have been heightened by the attacks. Those included a shooting in the makeup area of a Macy's store near Seattle, where five people died, as well as stabbings at a Minnesota mall where ten people were injured before a police officer shot the assailant.

Justin Dye, 41, of Huntingdon Valley, Pennsylvania, said he has felt more on edge when he goes to his local mall.

"You're not paranoid. But you are alert of the people around you," he said. The father of two said he now looks for where the exits are, and in a store he scouts for dressing rooms or back offices should he need to hide. "I'm always thinking about if something could happen, where would I go, and what should I do?" he said.

The recent attacks are "awful tragedies," and at the top of retailers' minds, said Lisa LaBruno, a senior vice president at the Retail Industry Leaders Association trade group. She was attending an already-scheduled meeting about security this week with store executives. "They are committed to reassessing the situation and identifying ways in which they can mitigate risks."

Still, she and other industry experts acknowledge that mall and store operators don't have much control over actually stopping any incident from happening. They do say they hope to minimize any threat and focus on keeping people safe.

Shopper surveys done every April by the International Council of Shopping Centers show that people aren't interested in metal detectors or similar tactics, the trade association said. "They don't want to be impeded as they go about their lives," said Malachy Kavanagh, a spokesman for the mall association.

Dye's among those who doesn't want to deal with the hassle of metal detectors; he said he'd rather see more armed security guards at shopping centers.

The mall group spent $2 million to develop terrorism training programs after the Sept. 11 attacks in the U.S., and shopping centers have made more changes since then. A 2007 shooting in Omaha, Nebraska, when a 19-year-old man fatally shot eight people was an impetus for malls to alter their approach. Malls began working with the Homeland Security Department on plans for first responders enter the building to try to stop the shooter, rather than wait for backup as had been the practice.

In the past two years, retailers and malls have offered enhanced training for workers — some use videos of active-shooter scenarios; others have store associates act out the parts. At Macy's, for example, active shooter training has been a requirement for all employees since 2014. Mall operators are also running more evacuation drills, and are collaborating with police departments that may train at malls when they're closed.

Technology is key too, though experts say there isn't one single thing that can thwart an attack.

Kavanagh says Homeland Security officials are working with malls on testing cameras with facial recognition that can detect people with criminal records and also cameras that read license plates and send alerts if a criminal or someone on a terrorist watch is around. DHS is also looking at creating virtual walls in open spaces to block drones equipped with handguns and other weapons, he said.

"As technology progresses, there has to be a counter-measure," Kavanagh said.

Colin J. Beck, a sociology professor at Pomona College and author of "Radicals, Revolutionaries and Terrorists," said that it's hard to protect malls from being targets. But he says measures like automatic scanning of license plates and faces in public spaces open up "questions of infringement on constitutional rights and potential abuse."

Some measures had a bumpy beginning. Security robots made by startup Knightscope read license plates, can identify a vehicle parked in a certain location for too long or sense intruders at odd hours.

But the Stanford Shopping Center in Palo Alto, California, scrapped a pilot test of the 300-pound robots this summer after one of them knocked over a 16-month-old. (The toddler was OK).

Stacy Dean Stephens, vice president of sales and marketing at Knightscope, said the company has since made improvements and expects to have several large mall developers in California start using the robots later this year.

"We learned an awful lot from the incident, and have moved on," he said.

One of the most-used tactics is the mass notifications which can be used for weather, power outages or more serious scares. Pocketstop, a Dallas-based company that sends such notifications, said business among shopping centers is up 33 percent over the past 12 months.

While less than 1 percent of the incidents involve a shooting or attack, it's on top of stores' minds, said CEO Daniel Wagstaff.

By next year, the company will launch a notification service for customers using the mall's Wi-Fi. Wagstaff said the move is tricky.

"The last thing we want to do is promote fear in our consumer. We want people to be safe, but we don't want to scare people," he said.

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