unless it’s a city campus all in one building — is impossible.
What about cell phone text message alert system?
They said in the Presser they do send out Imessages.
I know of almost no professors who allow students to keep their cell phones on in class, so that wouldn’t work. (The overwhelming certainty that they then will text message their friends every damn day in class [I’ve had to take away cell phones from COLLEGE kids in classrooms and give them back at the end of class] outweighs the extremely remote possibility that we will be on lockdown IMHO).
Also, you’re assuming that even outside class, everybody will check their text messages at the right time in order to effectuate a lockdown. Many will, many won’t.
When you have many commuter students,a lot of them will try to get off campus before they’re stuck on campus.
Finally, college student immaturity being what it is (and seriously, people, it’s out of control immaturity on a level that I never would have believed before I started teaching this year), there will be a significant minority of students who will disregard any and all orders.