Using his own San Diego home (mainly the bedroom) for the setting and a pair of unknowns as actors, along with a third in two minor scenes, he sets up a story about a young woman, having been haunted off & on by a demon since childhood; at the start of the film she moves in with her boyfriend ("We're engaged to be engaged," he says, rather evasively.) for nearly a month of horrors.
In an attempt to figure out what's happening, the tech-oriented boyfriend rigs up a camera and other electronic stuff to record what goes on while they sleep - or try to sleep. The scares come in small doses - a door eerily moving - then escalates to noises beyond the bedroom, footprints on the floor, a chandelier swaying, a shadow on the door, the bedding moving - all indicating far more horror than the usual graphically exaggerated signs.
No blood letting, no slashings - the worst it gets is to reveal what look like bite marks on the girl's back. No screaming surround-sound horror music, just the thudding of footsteps on the stairs, the eerie underplayed noises that go bump in the night. The characters are so everyday normal that it's hard to get to know them as characters with any depth. As a result, what happens to them is the frightening building of tension and the little scare moments created to generate screams from the audience.