Paramount will release Paranormal Activity to home video on December 29, just in time to give you something to purchase with the gift card you got over the holidays. Both the DVD and Blu-ray come with the theatrical version of the film as well as an unrated cut that includes an alternate ending (presumably the original one). And the Blu-ray includes a digital copy of the theatrical version, so you can play the movie on your iPod and watch it while hiding underneath your covers.
The technical details are as follows, according to Paramount: "the DVD is presented in widescreen enhanced for 16:9 televisions with Dolby Digital English 5.1 Surround and Spanish 5.1 Surround (theatrical version only) and English, French and Spanish subtitles. The two-disc Blu-ray is presented in 1080p high definition with English 5.1 DTS-HD Master Audio and Spanish 5.1 Dolby Digital (theatrical version only) and English, English SDH, French and Spanish subtitles." You'll definitely want to take advantage of that surround sound to get the best out of the film, which features some terrifically eerie sound design.
Even if you've already seen Paranormal Activity in the theater, you should take another look at it on home video. This is one of those movies that works very differently depending on the way in which it's watched. Yes, it's a lot of fun as a communal experience movie. But given that it's shot in a home movie style, seeing it on a TV or computer is more appropriate to the the narrative. Imagine that it's real footage, a la the pretense of The Blair Witch Project, and you can view it as if you were investigating this "evidence" of the haunting. It's the same reason Cloverfield was as good if not better on the small screen.
Just pray that after you watch the film the doors in your house don't start locking on their own, like what allegedly happened to Steven Spielberg.