At the University of Minnesota, 101 of the university's 270 buildings have electronic access devices. A control center can selectively lock and unlock doors, send emergency e-mail and phone messages, and trigger audio tones and messages. Video cameras monitor 871 locations around the university, and radio networks link the university with police.
California State University in San Bernadino, about 60 miles east of Los Angeles, has experience dealing with emergencies. It was evacuated in 2003 because of wildfires and closed again last year because of high winds.
Officials now have an automatic phone bank that calls every campus extension in an emergency. The school also has a flashing electronic bulletin board at its entrance and a mass e-mailing system.
The university had already been considering a similar system for text-messaging. "What happened at Virginia Tech will certainly accelerate looking into these issues," campus spokesman Joe Gutierrez said.
Despite the safety reviews, nothing short of a total lockdown would ensure the safety of campus communities, said Maj. Frank Knight, assistant chief of police at East Carolina University in Greenville, N.C.
"Stopping an individual with a weapon from getting on campus is nearly impossible," he said. "We can't ever guarantee the security of the campus 100 percent."
Associated Press writers Doug Whiteman in Columbus, Ohio; Ben Greene in Baltimore; Mike Baker in Raleigh, N.C.; Michael Tarm in Chicago; Nafeesa Syeed in Des Moines, Iowa; Maryclaire Dale in Philadelphia; and Michelle Locke in Berkeley, Calif., contributed to this report.