Eddy Salazar came up with the idea for the script when he caught someone breaking into his house after a meeting was canceled. That night, Salazar didn't sleep at all, thinking about what could've happened if he, in fact, went to the scheduled meeting. For the next two weeks, he kept waking up in the middle of the night after hearing regular ambient noises, which led to writing the screenplay for the movie.
Eddy Salazar completely improvised the last phone call to Martha (Clare Grant). During filming, director Monty Miranda made several changes to the script, this necessitated this new scene where John Figg calls Martha and leaves her a defining voice message that leads to the climax of the movie.