U.S. schools have ramped up security in recent decades, installing metal detectors and surveillance systems to counter a surge in shootings. New England saw one of the worst such attacks in 2012, when a gunman killed 20 elementary students and six adults at Sandy Hook Elementary School in Newtown, Connecticut.

James Alan Fox, a professor of criminology at Northeastern University, said a system like the one in Methuen could lead to fewer injuries and perhaps save lives.

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