The phones in the building go out, yet the little boy's mother is able to call the apartment and the phone rings.
When George stabs demonic Sally with a stand pole after she has chased him and Hanna down the rope onto the lower rooftop, Ulla's demonic corpse is nowhere to be seen on the lower rooftop where she was thrown by George one scene earlier.
The birthday cake shown at about 25 minutes into the film is not the same one we were shown at the start of the film, the hand-lettering is different, actually more legible than it originally was.
When Hannah is trying to block the door from the demon in the bathroom, the part of the furniture falls behind her, but in the next shot where she runs from the door, it's gone.
TV studio looks different when Hannah and George enter and when she is giving birth. In fact, the look of the scene changes multiple times. It's most obvious by watching the position of rotating light which keeps changing.
They are multiple issues with dummy's being used with George and the woman that is with him on the elevator, watch as George is climbing up the elevator wires, and kicks the possessed women in the face, when she is seen falling, it's clearly a
a poorly dressed dummy and not the lady in the elevator. Also, the scene after George's wife rescues the couple from the party, and the male turns into a demon, George fights him and pushes him over the stair railing, the shot of the male demon falling is clearly a dummy and not a actor doing the stunt.
Really obvious fake glass when a demon grabs a woman and pulls her out through the windshield.
When a guy makes a jump with the car in the garage near the end of the movie, you can clearly see the ramp which was used for the stunt.
The fake head used to turn Sally into a demon is clearly scene in a close up shot of Sally, as the head looks very awkward and moves unnaturally. More obvious in higher definition.
When the phone rings at Sally's birthday party, the receiver is clearly on backwards, which would prevent the phone from ringing. The phone is put back on backwards after the call.
One of the male gym members (he even has a line at 46:13) who is seen frequently (either working out, trying to break out of the building's top floor main entrance side by side Hank the gym instructor or in the garage gathering stuff to block the three demons from entering) disappears after 54:03 (he's facing the flame engulfed door, his backside to the camera pointing through the open car door) during the later garage scene demon/horde battles.
When street party is shown, a shadow of the cameraman can be seen when some kind of a menu with fruits is shown.
It is established that George and his wife took a class, that taught them how to
repel down a building and escape in case of fire. Yet, none of the tenants seem to remember this, and they let themselves be killed or be possessed by monsters. Assuming that George and his wife took the classes, most if not all the tenants should have known after taking the same class, how to escape, and more should have made it out alive then the movie depicts.