Good concept for a movie but
I think the writers could've put a little more thought into the story to make it more plausible and realistic. As many have pointed out, many things in this movie didn't make any sense making suspension of belief harder to accept. What makes a movie effective and "scary" is when viewers are able to put themselves in the situation and think "this can happen to me or anyone in real life".
Again, the writers had the right idea but was too sloppy with the details.