Colleges and universities, ever more mindful of campus safety, are installing outdoor sirens. The systems can blast spoken messages or tone alerts of danger--and one of the preset messages on many of the public-address systems warns: "There is a shooter on campus. Seek shelter immediately." As college officials reviewed their emergency-notification strategies in the wake of the deadly shootings at Virginia Tech last spring, many decided to install outdoor public-address systems. The Virginia Tech tragedy, in which a student killed 32 people before committing suicide, led administrators to think about how they would communicate with their diverse mixes of students, professors, and staff members if a similar tragedy took place on their campuses. One popular answer has been to install complicated digital systems that beam text, e-mail, or instant messages to thousands of registered users. But many officials have come to realize that not everyone on a campus would be at a computer or a cellphone at a given time. Thus, many colleges have decided that the old-fashioned approach of using sirens should be part of the mix of emergency-response technologies. Companies originally designed the high-powered systems to be used on military bases, or at industrial plants where hazardous spills were possible. Systems can be expensive, and some administrators note that the outdoor sirens do not do a good job of getting a message to people inside buildings, since the sound does not always carry through walls. Although siren systems may not work for every college, for many campuses, it is a relatively easy way to bolster response as part of a broader emergency-alert system.