This is a nice little chiller that sags a bit in a middle, and there are a few touches that raise questions that are never answered, but it otherwise fairly well done. (It was based on a two-sentence story, which I will post below... but don't read it until after you've watched the film.)
Also--and I never thought I'd say this--but it's refreshing to see this sort of story NOT feature a young hottie in her undies and/or nightie. Maybe I've watched waaaay too many of these short-shorts over the past few years?
Knock Knock (2014)
Starring: Akansha Sukhija
Director: Simrat Sandhu
Rating: Six of Ten Stars
And the two sentence story the film is based on: "I woke up to hear knocking on glass. At first, I thought it was the window until I heard it come from the mirror again."