Unless you’ve been in a sensory deprivation chamber for the past month, you’ve heard there’s some horror movie named "Paranormal Activity" ruling the box office. It was made for, like, $10 and has grossed $1 billion or something.

The real numbers are much more modest than that exaggeration, but make no mistake — "Paranormal Activity" is in the midst of a supernatural theatrical run. It has become a legitimate phenomenon.

This movie’s profit margin is the sort of holy grail studio bosses would kill for — and that might not be an exaggeration.

Director Oren Peli filmed "Paranormal Activity" independently for about $11,000. That’s less than the caterer’s budget on most movies. It’s even less than the budget for "The Blair Witch Project," the movie with which "Paranormal" will inevitably be compared. Paramount then bought the rights to the film for $300,000.

It first hit theaters a month ago, playing on only 12 screens but earning $77,873. Three weeks later, it earned more than $19 million on 763 screens for a per-screen average of $25,700 — matching exactly what "Transformers 2" averaged in its first week. The difference is, "Transformers 2" cost almost $300 million to produce.

Then "Paranormal Activity" slew the latest installment of the horror genre’s most tired franchise this past weekend, earning more than $21 million on 1,900 screens versus just $14 million on some 3,000 screens for "Saw VI."

"Paranormal" will almost certainly solidify its place in movie history by winning this Halloween weekend, since this week’s only other wide release is the Michael Jackson documentary "This Is It," which now seems sad if not tasteless.

The movie isn’t performing well because of an original story. "Paranormal" covers the same ground as every haunted house or possession movie. Young couple Katie (Katie Featherston) and Micah (Micah Sloat) have the misfortune of hosting a menacing supernatural presence in their house. The encounters begin with voices and ... let’s just say it gets worse.

It is receiving much praise for how it was filmed, but the technique is no longer innovative. All footage was supposedly captured via amateur video, and the film is presented as if it’s merely a compilation of the most interesting moments. We’ve seen this conceit in "Blair Witch," "Cloverfield" and "Quarantine," and that’s just a few of the American examples. So many movies have now used the "shot on amateur video" concept that it’s becoming a cliché.

No, what makes "Paranormal Activity" work so well — and it does work — is the same thing that works in all great horror stories. It also happens to be what the makers of torture porn like "Saw" and slasher movies like "Friday the 13th" have forgotten.

The scariest moments emerge from the unknown, and suspense is the product of expectation rather than actual violence.

Katie and Micah set up a video camera in their bedroom in order to investigate the strange activities they’ve been experiencing. Most of the action takes place at night, and the camera is usually in the same position. We see their bed on screen right, but we have a view through the doorway and down a hallway on screen left. When the lights go dim, we find ourselves squinting to see what might lurk down that darkened hallway. Seeing little is much more terrifying than seeing everything.

The movie then unravels toward its climax at a painfully slow pace.

Any hack can rush to cut off body parts. It takes a much more skillful hand to gradually grind an audience into the kind of delectable suspense that "Paranormal" achieves.

Now, let’s do maintain perspective. "Paranormal" falls into many of the standard horror clichés. Note the couple’s increasingly flimsy excuses for filming everything and for staying in the house. Don’t expect a movie that re-writes all the rules.

However, this is one of the few genuine experiences you’ll have at the movies this year, and that’s the reason for all the buzz.