According to a report from Rolling Stone magazine, Taylor Swift used facial recognition technology at her concerts to search for known stalkers in the crowd. She literally knew if you were trouble when you walked in.
Her record-breaking reputation Stadium Tour attracted tens of thousands of people per night -- so how did she pull off such a feat? Apparently, kiosks showing exclusive tour footage outside the venues secretly scanned the faces of fans as they watched. "The images were then transferred to a Nashville command post, where they were cross-referenced with a database of hundreds of the pop star's known stalkers," Rolling Stone wrote.
Swift currently has hundreds of known stalkers -- one actually showed up at her house with guns and ammunition, once -- so we totally understand going to such extreme lengths to keep her [and everybody else!] safe.