In the book, Robert is smart enough to cover the outside of his house in wire fencing, and he burns down the two buildings next to his so the creatures couldn't climb them and jump onto the top of his. Robert spreads lights around his house and exploding cars, but obviously he didn't think about what would happen if they got past both of those and decided to take his chances. It would have been helpful for him if they kept those features from the book, hmm?