If you’re a horror fan who loves the thought of ghosts and other supernatural forces, then you’ve probably seen Paranormal Activity when it was released in theaters on September 25, 2009. If not, then you’ve certainly heard of it. It’s a horror indie film directed by Oren Peli, but he didn’t just direct the film. He’s also the writer, co-producer, and editor.

The movie opens with a deceptive, yet chilling caption by Paramount Pictures thanking the families of Micah Sloat and Katie Featherston and the San Diego Police Department. Much like The Blair Witch Project, this intro tricks the audience into believing that not only is the footage they’re about to see real, but also that the aforementioned “characters” have perished. It sets the tone instantly, instilling the audience with a sense of dread for what’s to come. Katie and Micah are a young couple who are haunted by what seems like a ghostly presence shortly after moving into their new suburban home. According to Katie, she’s been harassed by this ghost since she was eight years old.

As a result, Micah buys a camcorder in hopes of capturing what he hopes is some cool footage of Katie’s supernatural tormentor. Before the haunting begins, Katie and Micah seem like a normal everyday couple—real people who might make vlogs and post them on YouTube. And while Katie takes this haunting seriously, Micah is skeptical. However, this force of nature turns out to be more than they can handle after a psychic tells them they may be dealing with a demon entity. The terror increases as the hauntings switch from creepy sounds and moved objects to more sinister activity, such as slammed doors and full-fledged possession. A possessed Katie eventually kills Micah, and the film ends with captions telling us that Micah’s body was found by police, while Katie was nowhere to be found. Copyright claims at the end let us know that, thankfully, it’s just a movie after all.

Peli produced this movie with a budget of $15,000 and cast two unknown actors as the co-stars. The film was employed in the found footage genre and the actors used their real names. It was shot in the style of The Blair Witch Project and managed to accumulate a striking $193.4 million worldwide.

The success of Paranormal Activity is mostly thanks to social networking. It began as a small indie film that earned a showing at L.A.’s Screamfest in 2007. Audiences were terrified. They blogged about the film, but it didn’t have a studio to back it.

Over the course of the next 18 months, Peli met Jason Blum, a producer who had previously turned down The Blair Witch Project. Blum invested in the film and Blumhouse Productions was launched, with Paranormal Activity going on to become the company;s first international success. Blum got a copy of the movie to Steven Spielberg, who was deeply disturbed by the film and became one of its biggest advocators.

Paramount Pictures then acquired the film for $350,000 and altered the ending. The movie was first shown at a few select college screenings. Then, taking a page from Blair Witch’s marketing campaign, Paramount created buzz on Facebook and Twitter to turn the film into a trend. The studio gave fans the opportunity to have the film shown at their local cinema by creating a “Demand-It” campaign on Eventful.com. Paramount promised a wide release if a quota of a million demands were met. There was also a “Tweet Your Scream” campaign where frightened fans posted clips of themselves screaming at scenes of Paranormal Activity. Worldwide, the film’s rights were purchased by international distributors from 52 different countries.

Paranormal Activity wasn’t just inspired by Blair Witch. Peli took inspiration from Open Water, a survival horror thriller, and the iconic 1970s British TV comedy Fawlty Towers. In particular, he liked the dynamic of the relationship between the two characters. According to him, the characters “… have the freedom to say what they like to one another because they’ve been together for so long.” That same authenticity is expressed in Paranormal Activity between Katie and Micah, whose scenes were heavily improvised.

Equally inspired by his own experience with ghostly activity, he aimed to make a movie centered on an invisible, yet malevolent, spirit. The spirit’s looming presence is made evident though Peli’s usage of static shots and long intervals of silence. The audience’s imagination is left to do the rest. With powerless characters and an undefeatable antagonist, all we can really do is fear the worst.

I would say Oren Peli’s method is highly effective. Even knowing the film is purely fictional, you can’t help but feel freaked out. It’s practically a no-sleeper. And if you’re plagued by the sense that something lurks in every dark corner afterward, then Peli considers his work a job well done.