Red Alert: In the Imperial Navy, played with realism (also with the Most Annoying Sound, inasmuch as the alert klaxon is custom-designed to irritate the nerves of every possible sophont listening, simultaneously):
“General quarters! General quarters! Set condition one throughout the ship! This Is Not A Drill!”
The Admiralty, Core Command and the Theater Commands in particular, prefers to use Defcon Five as its system, as do the Imperial Emergency Management Authority for states of civil emergency, and the Imperial Security Executive for local security warnings (a.k.a. our “terror alerts” and their “recommended paranoia levels”).
Military installations, the Constabulary, the EMA, hospitals, etc., do often have a bunch of color-coded response codes (“alerts” and “conditions”) to instruct everyone exactly which immediate situation they ought to be responding to, however, so the “emergency squad scramble” aspect of this trope is played straight.