The book Micah consults is a 1971 trade paperback from Dover Publications titled "Picture Book of Devils, Demons and Witchcraft", by Ernst and Johanna Lehner.
Filmed for USD$15,000 and grossed USD$9.1 million in its first week in the US, breaking the record of highest-grossing weekend ever for a movie playing at less than 200 theaters.
Oren Peli got the idea for the movie from a personal experience. Late at night he was sleeping and a box of detergent fell off the shelf. The box was pushed too far back for it to just tilt and fall.
Paramount Studios utilized paranormal researcher, Christopher Chacon, who is recognized as one of the world's foremost experts on paranormal phenomena, to promote and publicize the film. Chacon also works in the entertainment industry as a writer, director and producer.
Shown as a "Surprise and Mystery Film" during the 23rd Leeds International Film Festival's "Day of the Dead III" horror film marathon (7th November 2009).
Katie Featherston and Micah Sloat were reportedly paid just US$500 each for their performances. But due to the success of the film, the director, Katie and Micah are now renegotiating the amount.
Oren Peli spent a year redecorating his house prior to filming; the walls were originally stark white in every room and there was no railing to the staircase.
Dreamworks wanted to remake the movie with a bigger budget and better known actors rather than release the film as it was and use the original as a DVD extra.
The role of Dr. Johann Averies was cast with a real Paranormal Investigator from the Independent Investigations Group, Spencer Marks. The role was shot to help explain certain anomalies in the film. The role was predominantly mentioned in the movie, but the footage never used.
The guitar that Micah (Micah Sloat) plays towards the beginning of the film is a "trans blue" Line 6 Variax 700 six-string electric guitar. The guitar, created by amplifier manufacturer Line 6, was one of the first in a line of pickup-less electrics (meaning the electronics are internal) and features the ability to model or mimic "up to" 25 different stringed instruments including the distinct sounds of a Telecaster, Stratocaster and full hollow body electrics.
Survivor runner-up Katie Gallagher was originally cast to play the role of Katie, but was laid off because Oren Peli decided she was too "well-known" to keep the film as real as possible. Coincidentally, both Katie Gallagher and Katie Featherston have the same name as each other, and the main character.
The scene where Micah shows Katie the Internet page about Diane originally showed a lengthy online video of the exorcism; the scene was cut down significantly.
The knife Micah is wielding when talking to Katie during the making dinner scene at the beginning of the movie is the same knife he is killed with in the alternate ending.