Stephen King in "Danse Macabre" listed three types of scares: terrify, horrify, and the gross out. Not to say that Mr. King is not a master of his craft, but I wish to add one more level of scare and that is the cheap scare. What makes this different from the others is that it does not actually have to be scary. It's when the film maker purposefully manipulates the viewer to jump in their seats no matter how silly the pretext. The best example of the cheap scare is old cat jumping from out of frame onto one of the characters. Sometimes it seems cats rain from the ceiling in horror pictures, but no matter how many times you see it you still jump.
The Paranormal Activity series is the Alfred Hitchcock of the cheap scare. Whether you like these films or not you will jump, you will almost spill your drink, and your heart will quicken. This is quite an achievement considering that the series is based on bad photography and something you never see. The characters tend to be as flat as card board, and the plot is pretty much non existent. For all that, these films just work remarkably well. It's like a bunch of psych majors were put in charge of making a scary film. They work like clockwork.
The third film is pretty much exactly the same as the first two. A family suddenly gets an unwanted visitor in the form of something invisible and malicious. In this portion it seems drawn to the little girl of the family and the parents form the two poles of horror movie stupidity. The mother seems to want to ignore the whole thing, and the father who's a video camera nut wants to record everything. So between the two of them nothing gets done for about 3/4ths of the film. Look, I don't want to belabor the point but to paraphrase from Eddy Murphy, "When the house says 'Get Out,' then get out!"
The best thing about this installment is that the video nut takes apart one of those fans that go left to right and then puts a camera on top of it. We have long scenes of a camera slowly panning left then right. Left then right. Then just put something scary on the left, and the audience hates it when the camera starts moving right. You can almost feel the psychic wave of "Don't move! I want to see more!" Then on the right is some family member completely innocent of the threat. Then the camera moves left, but the scary thing isn't there anymore. Then it moves right and the scary thing is right behind the family member. It's a formula for a nitro fueled nightmare machine. I envy the geniuses who thought of it.
So, these films are shallow but they work and they work well. If you need a scare this is your puppy to be sure!