The film was shot entirely with hand-held cameras or steady cams. Every shot has some camera movement.
During filming, in order to get an actual reaction from Liv Tyler, director Bryan Bertino would tell her where to expect a loud bang from, but would then have the loud noise come from a completely different direction.
According to director Bryan Bertino, the film is partially based on an incident he experienced as a child. One evening a stranger came to his door, asked for someone who was not there, and left. Later, Bertino found out that other homes in his neighborhood had been broken into that night.
The film was shot in chronological order.
Many theaters across the United States were sent faulty reels of the movie, containing sound problems, which made a few minutes to several scenes of the movie filled with nothing but static. Most audiences did not realize the sound was a problem, since the dark overtone and loud background music in some scenes make the static seem part of the movie.