VIDEO: 'Paranormal Activity 3' trailer

It's become a Halloween tradition not seen since, well, "Halloween."

The "Paranormal Activity" series is back for its third try at scaring the pants off of viewers. And now there's a preview out to get fans in the mood.

This time around, the film is a prequel that examines the origins of the ghosts and spirits that torment sisters Kristi (Sprague Grayden) and Katie (Katie Featherston). The film takes place in 1988 when the two are young children.

The first two from the series have grossed a combined $370 million on a collective budget of only $3 million. So it's no wonder producers were eager to make a third.

The film is set for release Oct. 21. For those who can't wait until then, Paramount is running a Twitter-based contest to determine which city will see the film even sooner.

Here's the preview...