My last job was doing websites for higher education, and I can tell you that it's very much a thing. It's a part of many universities' emergency protocols, sometimes paired with an alert banner on the homepage. (And that banner may or may not link to a further page of information.)

While things like a gunman on campus is most certainly an emergency, these systems also serve other messages. Things like other emergencies (earthquakes, for example), snow days, we're just testing the emergency alarms today, etc.

Edit because I had another thought: the whole field of emergency preparedness in higher education is rather fascinating. Most of what I found interesting I had heard second-hand from clients, but you might find it quite interesting.