Behind the scenes, however, the mall industry continues exploring new ways to meet the complex challenge it faces: protecting huge areas designed to be accessible to thousands of consumers without scaring them off.
"It's a logistical nightmare," said Micah Carlson, a project manager at the National Security Technology Department of John Hopkins University's Applied Physics Laboratory.
Carlson and his colleagues are working on a project to determine which sensors for biological, chemical and explosive agents can work in large indoor spaces like malls -- especially which sensors may be prone to false alarms.
"There are serious ramifications to pinning grandma down on the floor when she has just taken a nitroglycerin tablet," Carlson said. "It's really not good for business."
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