To an unaware observer, everything appears perfectly normal. Either no one's around, or everyone's going about their business as expected. There's no reason to think there's any danger nearby or that anything is out of the ordinary.
But there's one tiny little detail that suggests otherwise. Something out of place. Something... amiss. It could be a moved piece of furniture, an insistent background noise, or a bit of speech or behaviour that is vaguely wrong. Whatever it is, it's so innocuous that our hero doesn't think much of it at first.
But at some point, the character has a sudden realization: that detail is a sign of imminent danger. And sure enough, that danger will manifest itself within seconds. The character will either be captured or killed, or will survive through fighting, escaping, or ducking that giant log right before it smashes into the wall.
To qualify for this trope, the detail must be unremarkable outside of story context, and must signal an imminent threat. Due to the Theory of Narrative Causality, that threat will not materialize until the character has made the link — even if the hidden ninja assassin could have sliced his head off as soon as he walked into the room.
Sometimes preceded by It's Quiet... Too Quiet. See also The Anticipator and Five-Second Foreshadowing. If the danger in question is a bomb, expect a Pre-Explosion Buildup. Compare A Glitch in the Matrix, Out-of-Character Alert, That's No Moon!, Bad Vibrations, *Drool* Hello. Contrast Cat Scare.
The Laser Sight and Crosshair Aware tropes are almost invariably used to provide characters with an Imminent Danger Clue, even when there is no in-universe rationale for their use, so much so that listing each example here would be redundant. It's the reason that the majority of fictional snipers use laser sights, for example, despite how counterproductive it is. Otherwise the only way to give the characters warning enough to survive a sniper attack would be a missed first shot, which undermines the threat somewhat.
- In The Godfather Michael realizes there is a bomb in his car when he sees his bodyguard Fabrizio sneaking away. Sadly, he is too late to save Apollonia, who had just gotten into said car.
- In The Godfather Part II, Michael anticipates his assassination attempt seconds before it happens because the bedroom curtains have been left open.
- In the original Total Recall (1990), Quaid realizes that the Recall doctor's explanation of the trouble he's in is a lie (and that they're about to kill him) from the fact that the doctor is sweating.
- Return of the Jedi:
- Wicket senses an unusual scent in the air seconds before a stormtrooper begins shooting at him and Leia.
- When Lando realizes that the Imperials are jamming their sensors, despite the fact that the attack should be a complete surprise, he immediately concludes that the shield is still up, allowing the fleet to narrowly avoid crashing headlong into it.
- In Star Trek II: The Wrath of Khan, Chekov finds a buckle that says "Botany Bay" and instantly realizes they're on Khan's ship seconds before they're captured.
- In Die Hard with a Vengeance, McClane (Bruce Willis) gets on an elevator with some fake cops. Because he was earlier in the film with some real NYPD cops who mentioned they always play their badge number in the lottery, he realizes at the last second that the fake cop next to him has the same badge number as the real cop. This is enough for McClane to kill them before they kill him.
- In The Debt, Rachel realizes that the ostensibly unconscious, Bound and Gagged villain in the next room may be escaping when the sound of raindrops hitting pots goes from a three-beat pattern to two (meaning the pot next the the villain's leg has been moved). She goes to check it out, sees the flipped-over pot, starts to creep closer, and promptly gets attacked by the villain, who was hiding just outside the doorway.
- In Terminator Salvation, the Mysterious Waif appears able to sense when the machines are about to attack. Since she's also a Cute Mute, her intuitions tend to be useless unless someone is looking at her at the right moment to notice her panic attack.
- In Captain America: The Winter Soldier, Steve doesn't notice anything amiss when SHIELD agents (including Rumlow) continue to get onto the small elevator he's in. It's only when he sees one of the agents (that's standing in front of him) with a bead of sweat running down his neck that he realizes something's wrong, and he immediately asks if anyone would like to consider leaving before the fight begins.
- In Kingsman: The Secret Service, as Eggsy and Arthur are about to toast the fallen Harry, Eggsy notices a surgical scar beneath Arthur's ear and realizes that he's had one of Valentine's loyalty chips implanted in him and is in on Valentine's plan. The realization gives Eggsy just enough time to pull a Poisoned Chalice Switcheroo on Arthur.
- In The Pelican Brief, Darby's teacher/lover was killed by a car bomb intended for her. She had refused to get in his car with him since he was drunk, and while walking away she heard the car's starter make an unusual noise seconds before it blew up. Later, when she and Gray are in his car looking over some recently acquired evidence of The Conspiracy, he turns the key and the starter makes the same noise. She catches it just in time to stop him from setting off the bomb, and they get out of the car and run from the assassins who planted it.
- The Predators cause one of these every now and then:
- They often subvert the common Laser Sight use. Rather than their targeting laser serving as a warning to the target, they either aim and shoot from an angle the target can't see it from, or they shoot before or just as the target notices, giving them no time to react.
- In the second movie, King Willie starts to suspect he's being watched when a brick tumbles off the top of a nearby building, and the Predator soon jumps down to the same spot.
- In the same movie it gets turned around on the Predator when it hears the wooden stairs in the slaughterhouse creaking as if under the weight of someone walking on them, despite having seen no one with its thermal vision.
- In the Expanded Universe, it's not uncommon for the distortion effect of the Predators' cloak or the sound they make when they breath to function as this; a character who doesn't know about them will at least realize something is amiss. A character who does know about them will immediately realize they have a very serious problem.
- In the Discworld novels, hoses and ropes getting tangled for no reason are a sign of Auditors approaching. (This might seem a bit odd, given that the Auditors are "the cold dead rules", and inexplicable tangling would seem to be chaos rather than order, but it symbolises the inanimate becoming malignant towards the living. And, of course, one of the rules the Auditors represent is entropy...)
- In A Clash of Kings, a character narrowly avoids being murdered by an "ally" on the battlefield in a subversion of Take My Hand:
"It was only at the very last, as their fingers brushed across the gap, that something niggled at him . . . Ser Mandon was holding out his left hand, why . . ."
- In Masques, Aralorn notices that a person her beloved is talking to lacks a shadow.
- In a Nancy Drew Files book, Nancy and a friend are setting out on a picnic when the friend points out a flock of birds that take off at the first sight of people. Later, as she and her friend are enjoying their picnic, the birds take off again. Nancy remembers what her friend said and realizes that someone's lurking in the bushes. She pushes her friend to the ground and dives for cover herself a second before shots ring out.
- In Alias, Sydney sits down with Francie and offers her a taste of cappuccino-flavored ice cream, which she gladly accepts. Sydney realizes immediately that something's wrong, because Francie hates coffee. Battle ensues.
- On Babylon 5, during any standoff with a warship, the shooting is usually immediately preceeded by a one of the Bridge Bunnies shouting, "We're picking up an energy spike!" Usually they aren't surprised in this case, as starships are usually pretty easy to see, but this is the announcement that the standoff phase of the encounter is over.
- Boardwalk Empire, in the episode "Two Imposters": Nucky tells Eddie to call Eli, Chalky, and Mickey Doyle. When Eddie tells Nucky the line is dead, he realizes Gyp Rosetti and his men cut the switchboard and are coming to kill him;. As a result, Nucky manages to fight off the first wave of Rosetti's men and escape to Chalky's place.
- In Crusade, Gideon and Lochley identify that an alien is about to shoot because the alien weapon produces a smell of ozone when it is being charged.
- Doctor Who:
- In "The Time of Angels", the ancient ruins they're in were from a culture where the population had two heads, but nobody notices for a while that all the "statues" have only one head each.
- In "The Girl in the Fireplace", the Doctor realizes something is amiss in a little girl's room when he realizes that the ticking sound he hears cannot originate from the room's one clock, which is broken.
- And in "The Day of the Doctor", the UNIT scientific team are standing in the middle of a statue gallery where every installation is covered by a large sheet when they realise the mysterious dust covering the floor is... the remains of the statues.
- In the Torchwood serial "Children of Earth," a character realizes she and her son are in danger when a neighbourhood dog stops barking.
- Sherlock: In "The Final Problem," John notices that the voice in the security footage of Eurus's psych evaluation belongs to the now ex-warden of Sherrinford, meaning he's under her control, as is the entire prison, and Sherlock, Mycroft, and John are trapped. When John voices this realization, he and Mycroft are immediately taken prisoner.
- Breaking Bad: A story arc in the first season involves Walter keeping Krazy 8, a violent drug dealer, locked up in a basement for days while he works up the nerve to kill him. One day, Walter loses consciousness while bringing Krazy 8 his sandwich, falling and breaking a plate. When he comes to a little while later, he cleans up the mess, goes upstairs, prepares another sandwich, and heads back downstairs. He and Krazy 8 then talk about their lives over beers and actually start to bond despite the situation. Eventually, Walter begs Krazy 8 to convince him that he won't murder Walter's family if he lets him go. Krazy 8 says he won't. This leads to Walter going back upstairs to get the key, relieved beyond measure. He throws something in the garbage and starts going back toward the basement... but a nagging feeling makes him go back to the garbage can, pull out the shards of ceramic from the broken plate, and re-assemble them on the kitchen table. Sure enough, a large, shank-shaped piece is missing, and he realizes that Krazy 8 took it while Walter was unconscious and has been planning on killing him upon release this entire time.
- Warehouse 13: The smell of fudge where there is no fudge indicates the presence of chameleon bombs
- In the Community episode "Modern Warfare," Abed notices a single line of paint trickling down a bathroom wall, steps back, sees the human-shaped bare patches above each urinal, and has time to say "Um, guys?" right before the female characters spring out of the stalls (and garbage can) behind them.
- Game of Thrones: In the final scene of "The Rains of Castamere," Catelyn Stark notices three of these just before the Red Wedding goes down. First, someone bars the doors. Second, the musicians begin playing a song whose key and content are inappropriate for the setting — none other than the episode-naming song, a Lannister song which only Catelyn recognizes. The final, threat-confirming clue is the reveal that Lord Roose Bolton is wearing chainmail under his clothes. Sadly, by the time Catelyn pieces all of this together and realizes that she and her family have been Lured into a Trap, it is far, far too late.
- Agents of S.H.I.E.L.D.:
- In "0-8-4", Ward's first sign that something is wrong comes when he realizes that the military squad on the Bus still have not touched their drinks even after several hours had passed, implying that there was something they planned to do that they needed to be sober for.
- In "Nothing Personal", while Hill complains about her obvious tails over the phone, she suddenly notices that they've disappeared or have been incapacitated. She immediately ends the phone call. However, the "danger" was just Agent May, who needed to chat privately with Hill so she could ask for her help.
- Daredevil: Karen realizes Colonel Schoonover is the Blacksmith when she looks at a photograph and recognizes one of the soldiers he's posing with is a body she just saw getting zipped up at the docks.
- The Punisher: In the season 1 finale, Billy Russo visits Curtis and tries to make him betray Frank. He accepts Curtis's offer of coffee, following Curtis around as he opens up the blinds in his living room/kitchen. Just as he's about to reach for the coffee mug Curtis is holding out to him, Russo puts together he's being moved to be taken out by Frank with a sniper rifle, and dives for cover just as Frank fires his first round through the window. In a matter of seconds, Russo also gets out his own gun and begins shooting at Curtis.
Billy Russo: YOU PEG LEG BASTARD!
- 2010 reboot of Medal of Honor:
- The first mission features a bomb rigged to a cell phone, which the men of AFO Neptune barely avoid at the last moment when they hear the phone ring.
- A Ranger squad is preparing to secure a small hut bordering on a potential landing zone for their helicopters. They don't quite make the connection, but they know something's wrong when they hear a phone right just before they are about to kick in the door.note
- The Legend of Zelda: Ocarina of Time: The fight with Dark Link in the Water Temple starts like this. Link enters a strange room that looks like an endless, ankle-deep expanse of water. In the middle of the room sits a small island with a dead tree. As soon as Link passes the island, his reflection is no longer visible in the water...
- Pokémon Mystery Dungeon: Gates to Infinity, your partner notices that the air seems to be growing colder. Unfortunately, Hydreigon is only able to confirm the fact before Kyurem ambushes them. It doesn't end well for the latter (Or the hero for that matter).
- The survivors in Dead by Daylight are alerted to a killer's presence via Heartbeat Soundtrack, with the heart rate increasing whenever they draw closer. If a killer is directly behind them, they'll also be lit up by a red light.
- Uncharted 4: A Thief's End: Nate, Sam and Sully have just beat Shoreline to an important location in the hunt for Avery's treasure, and are inspecting the site when Sam finds a spent cigarette butt on the ground. After he and Sully confirm that it isn't from either of them, they collectively realize that they didn't beat Shoreline there at all, and the mercenaries are just waiting to ambush them. Cue "Fire in the hole!"