Loud noises, especially unexpected ones, can be extremely jarring. Just as uncomfortable for many is the thought of dealing with uninvited guests, or accidentally letting someone untrustworthy into your house. When these two fears are combined, you can evoke fear from a situation as mundane as someone knocking on a door.
The noise won't stop for more than a few seconds at a time; if anything, it'll just get louder and faster, echoing through the house as the owner, rightfully, tries to avoid the confrontation on the other side. Sometimes the only way to get the knocking to stop is to open the door, which only leads to problems when the real fear comes from who is on the other side... However, even if they do go away, there's no promise they'll stay gone, or that they won't try and get in the house some other way. Sometimes, though, the knocking itself is the only issue, and it can even function as a Jump Scare.
Mood Whiplash follows if the person on the other side is innocent and trustworthy; more horror and mystery will ensue if it's discovered that there's nobody at the door. In most cases, though, the person at the door will be someone dangerous and untrustworthy, or at the very least, unwelcome.
Unrelated to The Last Man Heard a Knock..., but the story itself is an example of this.
- In Alice (The Non-Return), an Alice, Girl from the Future fanfic, the characters hear someone knocking on the door (while everyone else who lives in the apartment has keys and there's a doorbell anyway) and grow increasingly unsettled and scared. One of them suggests calling the police, but another points out that "Help! Someone knocked on our door!" won't be taken seriously. It turns out it's their good friend Alice, but with news of a catastrophe and a horrible murder.
- In When The New Year Trees Light Up, the forest animals' celebration is interrupted by loud and insistent knocking, and the animals jump to the conclusion it's the wolf out to get them. It turns out to be a hare who was late because she found two lost toy animals in the woods.
- The Fog:
- When the fog and the zombies reach the weather station, one of them knocks on the door. Dan the weatherman opens the door and looks out, allowing a zombie to enter and kill him.
- While Mrs. Kobritz and Andy are trapped in a house by the fog (and the zombies in the fog), one of the zombies pounds on the front door for admittance. Mrs. Kobritz foolishly opens the front door to see who's there and is killed by the zombie.
- Can be heard at the end of Mulholland Dr., when Diane sits alone in the dark of her apartment and gets startled by sudden knocking on the front door which culminates in a nightmare sequence. Watch the scene here (major spoiler alert).
- Happens several times in Howl's Moving Castle; justified, since after Sophie is scared half to death by a living scarecrow at the door, she gets alarmed every time someone knocks in fear of seeing the scarecrow again. Then the Witch starts an open war with the castle's inhabitants, and Sophie and Michael often get frightened she might start knocking on the door. All the knocking-related alarms turn out to be false.
- The trope codifier is the horror short story "The Monkey's Paw'', which climaxes with knocking on a house's front door by what is implied to be a horribly disfigured Revenant Zombie.
- In The Prowler, a children's book by Geoffrey Dutton, a neighborhood is terrorized by someone knocking at doors in the middle of the night, and whenever somebody is brave enough to open the door there's noone there. It turns out one of the neighbors taught her cat to knock to be let in, after he grew too big to fit through the cat flap, and he's been trying it out on everybody's door.
- The Raven opens with a late-night knock that first confuses, then frightens the bereaved narrator. The knocking continues for six stanzas, each making him more disturbed and uncomfortable- this lasts even after he opens the door, to find nobody there. Then he finds it was a raven knocking at the window, and things just get worse from there.
- In one of the Goosebumps books, the main character acquires a magic typewriter and starts Rewriting Reality. Setting the scene for a horror story, he writes that there's a storm, so it starts storming. When he writes that there's an ominous knock on the door, the same thing occurs... but nobody's there. He didn't write that anything in particular was behind the door, after all.
- Happens in the Buffy the Vampire Slayer episode "Forever", which is an Homage to "The Monkey's Paw", where Dawn attempts to resurrect her dead mother and is implied to have created a malevolent undead version of her. We don't see much of the undead mother except for a few flashes, but we hear a knocking on the door. Buffy tries to resist for a while and goes to open it, at which point Dawn finally thinks better of it and breaks the spell.
- Doctor Who:
- This trope features heavily for the final days of the Tenth Doctor, and a prophecy that "He will knock four times". This comes to a head in his final episode, "The End of Time", where this "he" turns out to be Wilfred Mott, knocking from within radiation capsule and asking to be let out... which the Doctor can only do by entering one himself.
- In "Hide", sinister knocking sounds are cited as one of the signs that Caliburn House is haunted. The knocking turns out to come from the Doctor himself as he tries to navigate the house within a parallel universe that is displaced in time.
- May I Please Enter: The Cowboy bangs on the door of the house he wishes to enter, and the moment lasts just long enough to become unsettling; despite that the audience is aware of who's at the door, they aren't aware of who is on the other side, or what the Cowboy actually wants to do inside the house.
- The Night Gallery's Pilot Episode. In the first segment "The Cemetary", two men are frightened to death when they believe a corpse has risen from the grave, walked to the house they're in and knocked on the front door. The first time it's a trick. The second time it's real.
- In Warehouse 13, A message was sent to Warehouse 13 saying "Knock Knock" before the lights went out and suddenly the door knocks. A new character has appeared: It's Claudia Donovan
- During the intro to EarthBound, the front door keeps being knocked on, over and over, with slow ominous music playing the whole time. Ness opens the door to discover Big Bad Friend Porky on the other side, who tells him about his brother Picky getting lost. After the game is over, the same knocking occurs on the door with the same music playing. When Ness opens the door this time, Picky is on the other side, leaving Ness with a note from Porky saying that Ness hasn't seen the last of him.
- In Chadam, we are first introduced to the titular character sitting alone in his house, when the sudden knocking at his door puts him into a state of dread and paranoia, which in turn makes the audience also feel tension at who is behind his door. Mood Whiplash occurs when it turns out to just be the young daughter of his friend, come to give him a picture she drew.
- Played with in Alantutorial, where one early video shows that something is very wrong in Alan's house when he's doing a paper-airplane tutorial, and we hear someone repeatedly banging at his door as he insists for them to stop so he can make his tutorial. However, it's not the knocking itself causing the scene to feel wrong...it's the fact that, due to the camera shaking as the knocking occurs, it's made very clear that it's Alan himself stomping on the ground to make the audience think someone is at his door.
- The Cry of Mann: Every single time someone knocks at the Mann family's door, it's played dramatically, as everyone in the room goes silent and stares at the door in fear as the knocking continues for several seconds. Each time, it drags on just long enough for it to feel just as worrying for the audience as it does for the characters, despite it usually just being the mail-man.
- Tribe Twelve:
- When Noah stays in a hotel for Halloween, one of the first oddities is the sudden knocking at his door, only for nobody to be there upon opening.
- One crossover with Everyman Hybrid has Noah be contacted by sociopathic Troll, HABIT, by letter. On the back of this letter are the words "knock knock", which is followed by immediate knocking at his front door. Noah goes to check the door...and gets transported to another room, where the knocking continues behind another door. He is visibly more shaken up as he opens this door, only to end up behind another door in another new room, where the knocking is even louder. Opening this last door transports him to HABIT's house.
- In The Sun Vanished: This happens several times:
- The protagonist tells his friend of a strange person standing completely still outside their house, and is told to not let anybody inside. Moments later, a video shows that this person went from standing like a statue, to knocking incessantly at the front door and even going so far as to jiggle the knob. This event leads the protagonist to stay hidden in their bedroom for two days straight.
- One case happened when the protagonist was hiding in their house, and all the information the audience got was through twitter; apparently, someone was banging at their door, and managed to break into the house when nobody answered.
- In another case, a video was uploaded of the protagonist answering the door; though the video was completely dark, the constant knocking was heard, following by the person at the door claiming the sun came back. In a following tweet, it was claimed that this person began to start banging again... on the window, with their head.