Chris Brittain undoes his lanyard to pull out a white card with a button on it. “Are you ready?” he asks the conference room full of administrators. Brittain, an assistant principal, pushes the button three times. An alarm goes off overhead on the intercom, signifying a drill on a summer day at Lenoir City High School in Loudon County. Brittain is testing a panic alarm system called Centegix Safety. It allows administrators, teachers and staff…