It's a well-paced, gradually established scenario; Norwegian writer/director Pål Sletaune keeps us guessing as to what is really going on, while drip-feeding information that slowly undermines the reliability of Anna's perspective.
Norwegian director/writer Pal Sletaune appears to have been influenced by Roman Polanski, but The Monitor is more oppressive than haunting. There is little or no sense of dread. The climax is predictable.
The movie makes less and less effort to keep us up to speed - it's a reasonable assumption that a lot of it's going on inside Rapace's head, but determining precisely how much feels like a fool's errand.