At the Warren's home, when their daughter Judy first notices the Nun, Lorraine gets up to investigate. Though taking place in 1977 on the bar is a bottle of Gentleman Jack whiskey. This was a label that was first marketed in 1988, and further, the bottle shown is a contemporary version.
Towards the end of the film, as the ambulance is being loaded, the camera pans upwards to show the semi-detached house once again. The house that forms the other half of the semi has uPVC double-glazed windows of a type not used before the 1990s.
The train the Warrens sit on near the end of the film is clearly a modern-day train carriage, complete with current reservation number style on the seats. In the 1970s most British Rail trains used the original Mark 1, Mark 2 or Mark 3 carriages, with more rudimentary luggage racks.
In the hallway scene after Janet ties herself to the bed and wakes to the door banging, she opens the door and calls out in the hallway. The next shot shows board games on a bookcase, and the game Bonkers can be clearly seen. The game was not released until 1978, a year after the film is set.
From the late 1960s, Marylebone station's covered cabway had large black-on-white British Rail signs reading "Marylebone" complete with a British rail logo in red and mounted across the road at each end of the roof. These were not taken down until the privatization of British Rail in the mid 1990s. They are absent in this film, set in 1977.
The width of the wall between the front outside door and the bay windows varies between shots. The wall width of the actual location shot is roughly five times smaller than the studio shot. This is noticeable throughout the entire film and is highlighted by the placement of the old leather chair and the size of the hallway.
When Ed goes to retrieve Janet from the closet, he burns his left forearm on a hot pipe. When he eventually gets her out and falls to the ground, the burn mark isn't there. Then, in a later scene, the burn mark appears.
When Maurice Grosse speaks with the possessing spirit Bill, the spirit plays the Knock, Knock game. Grosse is recorded as clearly pausing for a second or so before saying in a flat tone with a falling inflection, "Very well, who's there?" When the recording is later played by Father Gordon to the Warrens, Grosse is heard responding almost immediately to Bill and with a rising inflection. Even allowing for frequency shifts due to tape-recorder play-back speed, there shouldn't be an inflection change unless the played-back version is a different recording altogether.
In the middle of the movie, during a non-ghost activity kitchen shot, the Pyrex bowl on the top shelf moves slightly from one shot to the next. You can see the full pattern in the majority of the movie, however, it moves slightly, revealing where there is no pattern visible on the bowl.
In multiple shots looking down Green Street, there is a crossroads in the distance with a large red-colored raised speed table covering the entire junction. The real Green Street does not have this feature. The movie was actually filmed several miles away on a back street near Enfield Town.
The American investigators are seen arriving into London (and almost departing from London) at Marylebone station. In 1977, this station provided only a few regional services to Buckinghamshire and Oxfordshire, and certainly served neither of London's two transatlantic airports. At that time, trains to and from Heathrow were provided solely by the London Underground on a (then) brand new expansion of the Piccadilly Line, and trains to and from Gatwick ran (and still run today) to and from Victoria station.
In the scene where Janet is home sick from school, after she hangs up the phone with her mom who called to check on her, she uses the remote to flip back to the station she was watching, and the first station she flips to reveals an adult Jon Bon Jovi in mid-song. Since the story did not take place until 1977, Jon Bon Jovi would have been only 14 to 15 years old, a full 6 years before being discovered.
When the sound operator, sent by the polytechnic, is recording various sounds around the house, he points his microphone at an open door leading to the garden. He picks up the sound of crickets chirping. Since this is North London in late December, the chances of hearing crickets are virtually impossible.
No council house in Enfield has a cellar like that. Furthermore, if the property did have a cellar, the stairs would not be built or positioned like the way it is presented in the film. The cellar is clearly based on an American design - large and spacious - rather than the dark, damp and rather small cellars that London properties had in 1970s Britain. Those that weren't converted were filled with concrete due to flooding issues from the many underground rivers and sewers in the capital.
The scenes outside the school are filmed in present day. The school sign is showing an 11 digit telephone number with an area code starting with 012. At the time of the film, London numbers had the prefix 01, which was introduced in 1959.
Later in the movie, when Ed Warren asks her where the old chair came from, she said her ex-husband bought all the furniture with the house. Her ex-husband couldn't have bought the house as local councils didn't sell their properties in the 1970s. Also, local councils didn't supply any furniture when a house was re-let. Anything left behind by a previous occupant would have been disposed of before any new tenant moved in.
The layout of the house is very unusual for a UK property of this age. At the top of stairs is the bathroom, with a bedroom at back. The front of the house has a small bedroom over stairs and larger bedroom to the right of it. Also, the rooms are way oversized for the style of house shown at beginning of movie.
When Janet is hanging from the ceiling, her hair is following what gravity normally does. This gives away that the set is actually upside down and she is really on the floor. If she were stuck to the ceiling, her hair would've been down on her face.