These days, with cell phones and wide coverage areas available to everybody, horror movies set in contemporary times generally must set up a scenario where there is no cell service available in order to make their movie plot work, since otherwise anyone could just call for help and get rescued. But you know, people are so addicted to using their smartphones, when service is out, people can experience withdrawal symptoms and go a bit crazy, which is why I don't think horror movies that shut off cellular service really even need a monster or a slasher killer anymore. All they'd have to do is have cell service cut off, and have all the teens go insane and turn on one another due to cell phone withdrawal psychosis. And that horror movie would be called No Service. Or even Low Battery or No Bars would work for the movie title too.
In fact, No Bars would make a great joke horror movie-style ad for a cell phone company, like Verizon: young people would go hiking or camping, and they'd get freaked out by some abandoned cabin and noises in the woods, so they'd try to call for help, but they'd have no bars, and with no cell phone service, they'd all go crazy with fear, striking out at anything that moved, turning into a Lord of the Flies-type scenario; but just then, someone with Verizon would run across them in the forest and see their irrational, panicked behavior and know what was wrong: no cell phone service with their crappy carrier plan. So the person would approach them holding out their cell phone, and they'd all snap out of it and follow a Google map out of the woods. And then they'd all rush out to get Verizon. And the slogan could be: "No bars can trap you just like a cage. Break free of the 'no bars prison' with Verizon!"
