The fourth and latest installment of Paramount’s microbudget mammoth franchise “Paranormal Activity” killed it at the domestic B.O. Friday with about $15 million, besting a newcomer and a promising holdover that’s showing off its legs this frame.“Paranormal Activity 4,” the second series entry from “Catfish” helmers Henry Joost and Ariel Schulman, is looking to end up in the low-$30 million range this weekend, just a little behind the second installment but considerably trailing last year’s “Paranormal Activity 3″ opening of $52.6 million. This is a little lower than predictors pegged going into the weekend, and B.O. observers are attributing the slide to franchise fatigue and the fact that this frame’s slate is more crowded than “Paranormals’” bows have been in the past. Expectations aside, budgets for the films run notoriously on the slim side. With a cost of only $5 million for Par, the studio has already earned back its coin and just has promotional costs to recoup. Summit’s “Alex Cross,” based on the James Patterson novel and starring Tyler Perry, grossed $4 million on Friday. The thriller, the first to feature Perry without being helmed by the multi-hyphenate, is currently in fourth and is expected to earn a three-day in the low teens. Its aud composition — which may prove to be some cross-section of Patterson readers and die-hard Tyler Perry fans, decidedly different demos — will become clearer when demo data is made available tomorrow morning. Meanwhile, in second, Warner Bros.’ “Argo” dropped a stunning 13.6% to $5.1 million. The intellectual thriller has earned $31.7 million so far, and its remarkable hold bodes well for WB and the adult set in weeks to come. And in limited release, Fox Searchlight’s “The Sessions” opened on four screens with a per screen average of $8.5K. Pic will likely triple that through Sunday, as older auds generally avoid theaters on Friday night, landing roughly in the center of expert expectations.