Disregard the gimmicky marketing of Paranormal Activity. Yes, it is a bit inspired, with Paramount releasing the film in only a handful of cities, shooting a trailer that captures an audience’s reaction, and directing the unfortunate moviegoers who’d been left out to a Web site wherein they could “demand” it be brought to their town. Perhaps the studio really did tally the votes; more likely the plan was an old-fashioned slow rollout all along.

Either way, the buzz-building resulted in the late-night showings wedged into AMC Georgetown’s schedule the weekend of Oct. 2 selling out. (Even on Sunday!) And the bottom line is this: No amount of viral voodoo can sustain good box office if the movie sucks. (See: Watchmen.)

And Paranormal Activity definitely does not suck. It teases, it terrorizes, and it will burn images in your brain that will freak you the fuck out for days afterward.

The story involves a young couple who have recently moved in together. Katie and Micah (Katie Featherston and Micah Sloat, both believably natural) are attractive and happy, “engaged to be engaged.” Except for one problem: They suspect the presence of a supernatural being in the house, one that first started haunting Katie when she was 8. They consult a psychic (Michael Bayouth) but otherwise go DIY, buying a high-end video camera to record anything that might be going on while they sleep. Micah wants to goad the ghost into revealing itself to speed things along, but Katie is against the idea of even filming, afraid of making the situation worse. But the camera becomes a third character, capturing their discussion of the issue during the day and trained on their bed at night.

Paranormal Activity, which first-time ­writer-director Oren Peli made for $11,000, has logically been compared to the game-changing Blair Witch Project. Found-footage mocumentaries are so 1999, though, and this approach is the film’s biggest knock, with the “reality” of the situation highlighted with bobbing and weaving camerawork that gets nauseating fast. And really, what’s the point of this is-it-real-or-is-it-Memorex ploy? Everyone knows this didn’t really happen. And decades of horror films have proved that fiction can frighten quite effectively if done well.

Peli does it well. Most of the story actually takes place in pedestrian daylight, with Katie and Micah often quite funnily bickering about their options. Micah’s sarcastic and cowboy about it, disagreeing with Katie’s idea of bringing in a demonologist and saying, “This is my house, I’m going to solve the fucking problem, OK?” The audience sees only snippets of the nighttime footage, which always starts out quiet but with a time-stamp eventually showing the fast-forward to moments of activity.

It begins with little things, a creak here and footsteps there. But the activity worsens and the suspense builds, leading you to automatically brace the moment you see the couple asleep with text noting the date and time. And stuff. Gets. Freaky. Without giving too much away, Peli knows from creepy, borrowing a bit from horror classics but also demonstrating how shriek-inducing a person simply standing next to a bed can be. There’s no gore; there are no cheesy musical cues or cheap scares. It’s all just skin-crawling—until things come to a head. And then you may wish that Paramount went for a more retro gimmick from the days of monster schlock: Staffing each screening with “nurses” who could tend to the lightheaded and administer sedatives on your way out the door.