But I can't tell you, can't even hint at it, because the movie's shift in direction is so radical, its surprises deserve to be preserved. That's certainly what I would have told the folks who designed the poster, which shows what appears to be an astronaut walking the hallway of an Asian airport.
Does that help you?
Probably not, which is good.
The director, William Eubank, is a DIY icon, famous for having made "Gravity" before "Gravity," building a space capsule in his backyard and filming a stranded-astronaut movie (called "Love") in it.
"The Signal" gives him a bigger budget, which he fills with bigger ideas and ambitions, and bigger themes: the way technology empowers and entraps people, emboldening them to the point of arrogance.
And it's obviously cleverly designed. Subtle visual clues planted in the opening scenes - a little boy trying to pull a toy from a crane-and-claw machine - embellish and predict things that happen later in the movie.
"The Signal" is a sci-work of thoughtful hints and feints, but the movie's big reveal raises as many questions as it answers.
Such as: Is it time for Laurence Fishburne to stop playing mysterious sci-fi movie know-it-alls, especially when he's using this persona to sell Kias?
I don't know all the answers to all the questions in "Signal," but I think the answer to that last one is yes.