A common situation in a TV show with limited time to show events, where a character will suddenly appear in another character's home with no explanation. It can be interpreted as merely a shorthand to indicate that the character has in fact knocked and been let in but the scene is too boring to air. However, the trope often appears in contexts where that should not be possible, like when the person entering the house walks in on someone's private affairs, or is a villain, or is out of favor with the resident and walks in just to berate him, etc. Why nobody ever, at the very least, locks their door when they want to be alone is a great mystery.
This is particularly common in Role-Playing Games, which often allow the player character to simply wander into anyone's home at whim. Depending on the game, reactions can range from the house's occults being enraged at your intrusion to your being free to chat with whoever's in there without, for the most part, them seeming to mind your player character's presence at all.
Not to be confused with There Was a Door.
The Drop-In Character does this all the time.
- Fairy Tail: Every guild member walks into Lucy's home as if they owned it, especially when she's sleeping or taking a shower/bath, sometimes together with her. Hilarity Ensues because Lucy is not amused.
- Kannagi: Crazy Shrine Maidens: This happens all the time. The protagonist stopped locking his door after Nagi got to live with him (instead of, you know, giving her spare keys), and didn't lock the door when they both were inside as well. If people are ringing the bell at all, it is just that they are polite.
- Monster Musume: Agent Smith is fond of this. Her first appreance being showing up behind Kimihito in his kitchen.
- Negima! Magister Negi Magi: Negi wanders into Chisame's apartment while she's dressed as her alter-ego "Chiu-chan".
- Neon Genesis Evangelion: Brought up in the manga version. In one chapter, Misato is shown taking a shower with the apartment door left unlocked. Shinji walks in, realizes what's happening, turns beet red, and thinks to himself, "That's not safe! Anyone could walk in!"
- Pokémon had an episode where Professor Oak suddenly appears in the "new character of the week"'s family business (a greenhouse) to provide plot-important information; no one bats an eye.
- To Love Ru: Door locks are nonexistent. None. Zilch. Nada. Not on bedroom doors, not on the school roof, and definitely not on the washrooms, which results in many Accidental Pervert situations in the name of Fanservice and Rito getting the crap kicked out of him by pissed-off girls.
- The Simpsons: In one issue, Homer and Comic Book Guy are charged with obscenity. While the family is watching the newscast on TV, Comic Book Guy shows up, and when asked how he got into their living room, he launches into a rambling speech involving time-travel, teleportation, and other sci-fi elements... before admitting that their door was open.
- Watchmen: Subverted by Rorschach, as it's obvious that he broke the door and then waited for the owner to come home. Rorschach then criticizes the owner for installing such a cheap, flimsy Gordian Knot-brand lock.
- The New Yorker: A cartoon from 2002 has two agents walk into someone's house saying "We're from Homeland Security. You left your door unlocked."
- Zits: In one comic, Connie comes downstairs in the morning to find Pierce drinking coffee in her dining room. They had invited him to dinner that day, but he decided to show up early.
Connie: Was our door unlocked?
Pierce: Not at first.
- In one My-HiME Shizuru/Natsuki fan comic, Shizuru lets herself into Natsuki's unlocked room while she's asleep, and Natsuki finds her sitting across her table from her when she wakes up. Shizuru chides her for leaving her door unlocked, apparently from being tired from all the make-up work she's been doing, and Natsuki promises to be more careful in the future, but notes that no one out there is more "dangerous" than Shizuru.
- From Shizune's Perspective, a Katawa Shoujo fic, has an example in which the intruder is also the one who forgot to lock her door. Shizune walks into her own unlocked room to find Misha and Hisao having sex with each other; Shizune had no idea that they were in a relationship at all.
- The Jetsons: The Furbalows do this after their daughter follows Elroy home. It's downplayed a bit in that they enter the room only after announcing their presence from the open doorway.
- The Kids Guide to the Internet: Lisa and Andrew simply walk in to the scene. They were evidently dropped off by their mother, and the Jamisons have an open door policy because there was no knocking, doorbell or "Hello?"
- Not Another Teen Movie: Parodied. When one character asks another how he entered her house despite its locked door, he replies that he came in through a hole that got knocked in her wall earlier.
Janey: How'd you get in here? The door was bolted.
Jake: There's a giant hole in the side of your house.
- Rear Window: Lisa breaks into the suspected murderer's apartment and is caught by him when he returns. It's not clear what excuses she gives him for being in his home, but one of them is apparently "The door was open. . .", indicating that she's claiming that she thought someone inside might need help.
- Can You Spare a Quarter?: Neither Graham nor the other people on Valdez Island lock their houses, as it's an isolated island.
- Little Women: Aunt March frequently barges in, complaining about how her family doesn't lock their door.
- The Outsiders: Ponyboy explains that he and his brothers always leave their door open since you never know when a friend might need a place to crash, and they are rarely surprised to wake up and find some random gang member sleeping on their couch, or even a rival gang leader reading a newspaper while sitting in their chair, having already made breakfast.
Ponyboy: [wakes up, walks downstairs and sees Tim Shepard on the couch reading a newspaper. He obviously came in while everyone was asleep] ...Hi, Tim.
Tim: [without looking up] Hi.
Ponyboy: Can I... get you some breakfast?
Tim: Nope. [folds up newspaper and walks out of house]
- Angel: When Angel becomes CEO of the supernatural law firm Wolfram & Hart, Eve (his Liaison to the Senior Partners) keeps doing this to upstage him, except for one episode when she does this while Angel is taking a shower. At first Eve claims his door was open, then changes to "your door was unlocked". Then Eve admits she has a key. Which Angel wordlessly takes off her.
- Babylon 5: Londo returned to his quarters to see that his door was open. G'Kar was waiting inside, wanting to purchase a certain plant for a religious ceremony.
- Birds of a Feather: Parodied. Dorien has a habit of just walking into her neighbors' house. At one point, they lock the door. She smashes the glass panel next to the lock, undoes it, and comes in anyway, while they were standing right there staring at her in disbelief.
- Buffy the Vampire Slayer: This becomes a Running Gag in Season 4 when different characters keep wandering into Giles' home, with him lampshading by saying "I thought I locked that door." or "Now, I know I locked the door that time!"
- I Dream of Jeannie: Dr. Bellows frequently enters Major Nelson's house without even knocking. Apparently being in the US Air Force means your superior officer can walk in your front door any time he likes.
- Even Stevens: This is a Running Gag with the character Beans. Lampshaded in The Movie when the family is sitting down to dinner and Beans pops up, prompting Donny to say "This kid is starting to freak me out" and another character to propose changing the locks. Possibly averted by the fact that everyone found Beans weird and unsettling.
- Family Matters: Steve Urkel treats the Winslow house as his own. When asked at one point why he never knocks, he says that if he did, no one would let him in.
- The Flash (2014): Star Labs probably has revolving doors at the front and back of the building. Sisco lampshades the lack of security in the season 2 premiere, acknowledging that people could just stroll in whenever they wanted.
- Friends: when Monica and Chandler agree to move in together, Monica tells him to lock the door to her apartment, then unlock it again for the first time as her roommate. Chandler replies: "The door hasn't been locked in five years, but sure." Then in the final episode, Monica and Chandler leave their keys on the counter as they leave the apartment... and then so do all the others.
- Highway to Heaven: Jonathan occasionally does this to gain access to any difficult-to-reach character who was part of his assignment for the week.
- It Takes a Thief (2005) has two ex-cons who, with the owner's permission, and while videotaped, try to steal (then later return) things from the owner's house. They often gain access through unlocked doors. Then they help the owners improve their home security and try again some time later.
- Lucifer (2016):
- Lucifer himself lives in a luxury apartment above his nightclub, accessible by elevator. Judging by how many people wander in uninvited — from friends looking for him, to friends looking for stuff in his bedroom, to villains of the week — he doesn't bother to keep the penthouse floor locked.
- Lampshaded one of the times Lucifer lets himself into Chloe Decker's house:
Lucifer: The text said to meet you here.
Chloe: Yeah, it never said to barge in like you own the place!
- Married... with Children:
- In earlier seasons, Steve and Marcy have the courtesy to ring the doorbell when coming over to the Bundy's residence. After Steve leaves her, Marcy lets herself in whenever the scene calls for her to be there.
- Lampshaded when Marcy walked in through the Bundy's door and says "Why do you keep your door unlocked? Any crazed killer could come in and murder you?" Al's reply is "Yeah, like I ever get what I want."
- Million Yen Women: The women were invited into Shin's house without Shin's knowledge. The first to arrive, Hitomi, just let herself in while Shin was out, causing him to be completely freaked out when he came home. Hitomi herself points out that he should lock his door.
- MythQuest: Philthy walks in on people a lot, often coming surprisingly close to learning about The Masquerade. Cleo asks him if he ever knocks and his response is, "Hmm, no."
- NCIS: Any character that wants to speak to Gibbs when he's at home can, due to the fact that his front door doesn't even have a lock.
- Phoenix: In "Blessed are the Peace Makers", the Major Crimes Squad raid the headquarters of an outlaw biker gang in the middle of the night. Senior Sergeant Renford raises a huge mallet to smash the door down...then tries the handle and realises the door's unlocked, enabling them to sneak in and catch the bikers asleep.
- The Secret Life of the American Teenager: Done frequently. A notable example happened in the season one episode, "Maybe Baby" when nearly every regular character ended up in Amy's house, arriving in groups of two or three, just to tell her they would support her if she wanted to keep her baby. They have gotten better about it in later seasons (meaning it's more common to see people actually knock on the door and wait for someone to answer it) but it's not completely absent.
- Seinfeld: Kramer is based almost entirely off of this trope — he's neighbors with Jerry, often enters without knocking in a distinctive manner, and often steals food from the Jerry's fridge. This is averted with every other character — Jerry has to buzz George and Elaine into the building every time they come over, whereas Kramer lives across the hall from him.
- Subverted in one episode. Kramer's drop in style involves sliding through the doorway as he opens it in a practiced motion. In one episode, Jerry locks his door, causing Kramer to slam into it.
- In another episode, Elaine goes to visit her boyfriend and is surprised to find his door open. He claims "I like to encourage intruders".
- "The Robbery" — the third episode of the series and the first instance of Kramer's slide — Jerry discovers his apartment was robbed because Kramer left the door open after borrowing a utensil, intending to bring it back right away but getting distracted by a TV show. Jerry doesn't have insurance.
- Smallville: This happens so often that characters Lampshade it. Particularly nonsensical for Lex Luthor, who has cameras and security systems. This is a Justified Trope when Clark is involved, but not when it's, for example, Jimmy Olsen.
- Final Fantasy VII: Just about any random house in any town you visit can be entered at will, and you're free to chat with whoever's in there without, for the most part, them seeming to mind your player character's (usually Cloud's) presence at all.
- Knights of the Old Republic II: The Sith Lords: Lampshaded. If you visit one apartment on Citadel Station, the resident will come in as soon as the player starts opening storage containers, and he shouts at them for stealing his stuff.
- Golden Sun gets a special note for actually having bandits lampshade how people let complete strangers wander in and out of their homes at will and take advantage of a town's lack of home security to loot from the mayor, several homes, one of the protagonists and a holy sanctum.
- Persona 5 sees the protagonist and his friends sneak into his guardian Sojiro Sakura's home to find Futaba Sakura. When Sojiro rushes inside later at the sound of Futaba screaming, Ann explains immediately that the front door was unlocked—which it was. Sojiro sighes, commenting that it's happened before, considering how he's getting old.
- Super Paper Mario: In the opening cutscene, Mario and Luigi simply walk into Bowser's castle.
Bowser: What? My front gate was open?! How many times have I told those idiots?! If you're the last in, LOCK THE GATE!
- Trails Series uses this in a similar way to the Final Fantasy franchise. All of the games in this franchise are full of apartments and private homes. Your characters can pretty much just walk freely into any of them and chat up the residents, none of whom seem even the slightest bit bothered or surprised by the sudden presence of these people in their homes.
- Homestar Runner: The title character finds his way into Strong Bad's house on many, many occasions. Even though Strong Bad is outspoken in his hatred of him. At one point Homestar lampshades this by asking whether he actually lives in Strong Bad's house.
Strong Bad: Is there like a sign on my door that says, "Wanted: Everyone I hate. Inquire within"?
King of Town: [randomly walking in] I didn't see one.
- Aqua Teen Hunger Force: In one episode, Dr. Weird's latest invention is stolen away through the hole caused by his previous invention.
Dr. Weird: [standing in front of a gaping hole in the wall] Who could have penetrated my impenetrable fortress?
- Ben 10: Alien Force: Lampshaded in one episode when Kevin just shows up in Ben's room, having gotten into his house by punching through his door.
- Dragons: Riders of Berk: The Dragons: Race to the Edge episode "Family on the Edge" starts with Hiccup opening the door to his hut to find Dagur (his Arch-Enemy until their recent Enemy Mine episode earlier this season) just casually hanging out in his room.
- Phineas and Ferb: In one episode, Doofenshmirtz sets a trap for Perry the Platypus when he comes in, only for Perry to come in through the backdoor which the maid left unlocked.
- The Simpsons:
Chief Wiggum: These prestigious, wrought iron security gates are bulletproof, bombproof and battering ram-resistant. Now...
- In one episode, when Homer gets an illegal cable hookup, the cable guy comes by later with some stolen merchandise he thinks Homer might be interested in. "Your door wasn't locked in any serious way."
- "Reality Bites": The Springfield Police auction off the gate to Johnny D's mansion.
Principal Skinner: Then what happened to Johnny D?
Chief Wiggum: He forgot to lock them.
- Teen Titans Go!: Robin leaves the door open while cave-sitting the Batcave while Batman is out, and the remaining Titans just waltz on in.
- Winnie-the-Pooh: Pooh sets up an elaborate, if hasty, furniture barricade in front of his Front door and is patrolling it with a popgun rifle. He hears a knock and is nervously trying to ascertain the identities of his friends knocking at the door, when Tigger bounces on the bear, with Rabbit and Piglet walking in behind.
Pooh: How did you get past my Hunny-napper traps?
Rabbit: Your back door was open.
- A while back, Twin Cities police officers had a campaign where they'd go up to houses during the night, and leave warnings if the door was unlocked. Eventually, this led to a pair of officers not-quite-legally entering a house and waking up a homeowner to politely tell him that he is an idiot for not locking his doors, leaving his garage open, and leaving the keys in his ignition.
- Michael Moore also did this in Bowling for Columbine, in Toronto, just to show off the difference between how Americans and Canadians behave in regards to home security. It's not really true of course, in most parts of Toronto you would still be a huge idiot to leave anything unlocked.
- In the town of Churchill (Manitoba, Canada), it is considered common courtesy to leave your house door and car door unlocked, just in case a stranger needs a place to hide from a rampaging polar bear. Car theft is not considered a problem as the town has no roads linking to the rest of Canada.
- This practice is fairly common in many remote parts of the country (most notably in the northern territories). Doors are left open and keys are left in ignitions because a) The towns are small and remote enough that theft is not a salient concern and b) The communities are close-knit enough that it's more or less taken as common courtesy that if your neighbour needs to borrow something, they're free to just grab it from your house and give it back later.
- Crime shows that feature crimes that happen in such presumably safe communities will inevitably have someone declare, "People don't even lock their doors at night!"