(at around 23 mins) The mirror hanging on the wall when Tricia (Courtney Bell) is talking to her psychiatrist (Scott Graham) is the mirror from Mike Flanagan's short film Oculus: Chapter 3 - The Man with the Plan (2006) - also starring Scott Graham.
(at around 36 mins) When Tricia and Callie go looking at apartments around the midpoint of the film, the first empty apartment they visit was actually the very apartment that director Mike Flanagan lived in (with four other people) when he moved to Los Angeles in 2003. It was a complete coincidence; the unit just happened to be vacant, and Flanagan had no idea they'd be filming there until they arrived on location that morning.
Funded in part by over 300 donors on the crowd-funding website Kickstarter.com. The filmmakers set out to raise $15,000 over the course of their 30 day pledge drive, and ended up raising $25,000 (more than one third of their final budget).
(at around 1h 5 mins) When Callie and Tricia are reading the news about the three missing students, the text of the columns corresponds to an article about the music group One Ring Zero (written by Susan Carpenter and published in "Los Angeles Times" in June 10, 2004).
(at around 18 mins) When Callie is introduced to the detective Mallory before she excuses herself to go shower she says "nice to meet," clearly forgetting the "you" at the end of the sentence.