The whole movie takes place inside the house shared by a young couple, Micah and Katie (played, appropriately, by Micah Sloat and Katie Featherston). Micah has just purchased a video camera, hoping to find out what is responsible for the weird goings-on that occur while the couple is sleeping. He puts the camera on a tripod in the bedroom, then each morning peruses the footage with Katie looking for clues. At first, the images are little more than odd. For example, the bedroom door opens and closes a couple inches. Subsequent nights bring bigger events: loud noises, lights flipping themselves on and off, the sound of footsteps coming up the stairs.

There is a compelling dynamic between Micah and Katie. She has long been a believer in paranormal activity, and therefore believes it when a psychic tells her that some kind of otherworldly spirit may be attempting to make contact with her. Micah, on the other hand, views the strange events with a bit of disbelief. Even when there's some pretty hardcore evidence that something is in the house, he refuses to accept that it could cross over and harm either of them. Katie begs him to stop taunting the entity (with and without the camera) but he can't help himself.

Director Oren Peli has masterfully staged Paranormal Activity for maximum creepiness. When the couple goes to bed at night, we always see the same static shot: they lay in bed on the right side of the screen while their open bedroom door is on the left. You never know where to look. I found myself reacting as though at a tennis match, looking back and forth from the bed to the door, waiting to see what was going to happen and where it would take place. When Peli wants to you focus somewhere in particular, he knows how to do it. When you hear footsteps, you look toward the door. When Katie begins moving strangely in bed, you look toward her.

Paranormal Activity is a classic example of what I call a "dread movie." It's scary, yes, but more than that, it instills a strong sense of dread within you as you watch. That dread hangs over the whole film. Whenever it was nighttime and the couple went to bed, a queasy feeling entered my stomach; this is when the scary stuff starts. When it was the next morning and we were seeing Micah and Katie talking about what happened, I took a deep, relieving breath. Then it would be night again and I'd physically tense up. It's incredible how this movie plays the audience like an instrument.

About halfway through, I felt like I couldn't take it anymore. I wanted out. Let me stress that I mean this in a good way. Paranormal Activity becomes more intense and frightening with each passing night that Micah and Katie are in the house. Few horror movies are ever as disturbing as this one is at its halfway point. Knowing that 45 more minutes of ever-increasing terror awaited me, I felt the kind of apprehension that I've only felt in horror movies a handful of times in my life. I've never been afraid of monsters or masked killers on screen. It's the unknown or unseen that plays on my nerves. This movie practically has a PhD. in conjuring up the unknown and unseen.

I will not reveal anything about the biggest scares, except to say that their simple, concise staging is precisely what makes them so chilling. This is not a movie that needs elaborate CGI. It makes due with a sound effect, or a simple practical effect (like a bed sheet billowing), a basic object (such as a Ouiji board), or an effective performance. That last thing is really important. Both actors are good, but Featherston really sells the mounting panic and fear. She's as indispensable to Paranormal Activity as Heather Donahue was to Blair Witch, albeit less shrill.

When I first saw The Blair Witch Project in 1999, I didn't sleep for four nights afterward. Every time I closed my eyes, I pictured the film's haunting final images. Paranormal Activity has a final moment that is just as shocking and upsetting, but with more of a concrete payoff. I had no trouble sleeping last night because I blocked it out of my mind. However, when I think about it now, I still get little chill. I don't scare easily at horror movies, even good ones. Paranormal Activity goes on the short list of films that totally, completely freaked me out.

( 1/2 out of four)

Paranormal Activity is rated R for language. The running time is 1 hour and 39 minutes.