“Understand To Be Understood,” a play created by nine teenagers living in New York City homeless shelters, examines whether metal detectors in high schools protect or damage students’ lives. The play questions why detectors weren’t installed at Columbine High School after two students went on a shooting spree there in April 1999, killing 12 students and a teacher and wounding 24, the worst school massacre in American history. The play was written by its young acting troupe, above, and edited and directed by Juliette Avila. It was part of the New York International Fringe Festival, playing five dates in August at the Actors’ Studio on Seventh Ave. S.