Recent events involving active shooters on campus underscore the importance of promptly notifying the campus community so students, faculty, and staff can take protective action as the incident develops. This study (a) developed warning messages informing the campus of an active shooter that can be delivered to cellular telephones and e-mail accounts, and (b) assessed their effectiveness. Participants were 264 (76 men, 188 women) undergraduate students at Western Washington University who indicated their understanding of and anticipated responses to text and e-mail messages. Participants indicated that they understood the instructions and would take the actions indicated in the messages. The results indicate text and e-mail messages are effective ways to notify and provide coherent instructions to the community during a life threatening emergency. This approach may be modified to create templates for other emergencies and disasters (e.g., earthquakes, tornadoes).