All good superhero teams - hell, all good law enforcement services - need some kind of emergency alarm. Not everyone gets access to the one for Avengers Tower, of course, but it's still very much there. Its use is left to Fury, the President, and few other important people who get priority over everything and everyone else. To this day, Tony will deny making Pepper's anti-kidnapping signal on her watch connected to it, but everyone suspects it anyway.
But when the alarm rings at some ungodly hour, an entire series of reactions and reflexes tumbles inevitably towards the scrambling of the Quinjet and a full assembly of the Avengers.
Steve is the first one up, bolting out of bed, every sense immediately alert. A light sleeper from his days in the military, the surprise midnight drill is nothing he hasn't trained for. His sock-covered feet (and yes, he does sleep in socks) hit the floor in three seconds flat, his sergeant's voice still ringing in his ears. On your feet, men, double time, locked and loaded in five, let's move it. The weight of the shield in his hands, the familiar pull of the mask over his head, all of it is automatic, comforting and near-instant. After all this time, Steve Rogers' reflexes don't differentiate between a Skrull attack, a midnight drill or a German air raid.
Most of the time, Tony isn't sleeping anyways. He's still in the lab, downing his fourth cup of coffee, dizzy from sleep deprivation and covered in motor oil. The alarm will illicit a string of loud curses about having to be interrupted from his genius and his coffee. But Tony's costume is always the simplest to put on, in a strange way - one button, thirty seconds of clicking gears and the smooth grind of metal and he's done.
If Tony has been sleeping, the team has to call Thor or Cap to practically drag him from the bed and throw him at the wall, sometimes repeatedly. This will result in even louder, more profane curses, some half-dead stumbling for his suit changer and a desperate, "Tell me my coffee is ready or so help me I will cut off your luscious mane and make daisy chains from it to wear as a victory crown."
Usually, Steve has already thought to make the coffee by this point.
The two S.H.I.E.L.D. agents are usually sleeping in their separate rooms just across the hall from each other. The sniper and the spy, both light sleepers, both so used to jet lag, red eye flights and reconnaissance missions at odd hours back when they were S.H.I.E.L.D.'s wild card team that this hardly seems to bother either of them. Clint's habit of keeping his bow and quiver propped against the bed, literally within arm's reach, serves him well at such times. Natasha sleeps with her fingers curled around one of her pistols like an old teddy bear, the rest of her gear lying not five feet away. Clint jokes about how Natasha changes into her suit faster than he does - something about women taking forever to get ready - but he mostly accepts it as one of the many things at which Natasha is superior. He is secretly convinced that her mutant superpower is always looking perfect, no matter time or situation, but maybe it's just him.
Every so often, the blaring, mechanical sound will come on a night where shadows of the past have crept up on the sub-conscious of the sniper or the spy, when facing the darkness alone has become unbearable. On these nights, the alarm will find one of their rooms empty, the other occupied by the two bodies curled around each other like there is nothing else to hold onto. The outsider will rise without speaking and return to their own quarters, quick and silent as the killers they are.
Bruce will hear the alarm dimly, through some generally unpleasant dream, but knows he can wait at least five minutes longer than everyone else. He has no suit, no weapons, nothing to change into or protect him. The Other Guy will get his chance soon - very soon, if the emergency alarm is being used - but for now, Bruce holds onto this moment of humanity. Sometimes he pretends that it is not a supervillain or an international incident or Skrull army, but just an alarm clock. A very loud, obnoxious alarm clock that he can press the snooze button on and simply go back to sleep. This never works, and when the five minutes have elapsed, Dr. Banner rolls out of bed, cracks his neck, slips on a pair of pants, and resigns himself to it before the Other Guy has even woken up.
Thor is the last to awake, grumbling odd curse words and stumbling around blindly in the dark for Mjolnir. Steve will inevitably hear the loud thunk of the god's foot colliding with his hammer, followed by even louder cursing. In Asgard, no one would dare to wake the prince before midday unless he had requested it. Here, no such rules applied; in fact, Thor has begun to suspect that sleep on Midgard is truly optional, judging by the sleeping habits of his teammates. Nevertheless, once he finally closes his hand around the familiar handle, his armor follows automatically. Thor is the last to stumble into the living room, where Steve, Nat, Tony, Clint and Bruce are already nursing cups of coffee, being briefed on the situation.
At this point, the only thing worse than hearing Tony say, "Good morning sunshine," is, "False alarm."