In the UK they actually sound/flash alarms at locations and in the fire-station, do they not do that in USA? They do in the movies.
Still seems like an ironic choice, applies equally to the people saying it was DEFCON1. I'm pretty sure the military actually have displays indicating the status, but again that's based mainly on movies.
https://en.wikipedia.org/wiki/Multiple-alarm_fire
The 5th level or a five-alarm fire, is the top level where you're basically talking all hands on deck.