Last month’s responses to the report of an armed man on the Virginia Tech campus showed how drastically colleges have upgraded their mass-alert systems since a gunman killed 32 fellow students and faculty at the Blacksburg campus four years ago. When Cho Seung-Hui shot his first two victims on April 16, 2007, the university waited more than two hours to send an email of warning to the campus community.

On Aug. 4, 2011, three teenagers thought they spotted a man carrying a handgun at the school. Even though no such man or weapon was ever found, students and staff were alerted by text messages, Twitter posts, emails, sirens and flashing message boards within a half-hour of campus police being called.