Not so much because it's almost all shot on digital cameras that allow a stranger to terrorise James (Nick Stahl) when his wife (Mia Kirshner) suddenly disappears.
The who, what and why become irrelevant. Nobody believes him, especially since he never manages to actually come up with any evidence.
Running through all the tropes of the horror genre, the film becomes increasingly irritating by simply suggestion that there might be somebody out there watching you.