We bought this to keep stray cats out of our house. Unfortunately, the pet moggy which lives a few doors along also uses a magnetic cat-flap and has discovered that his magic magnetic collar allows him access to our home anytime he wants! Really nothing one can do about this. We've also found that if a big bruiser of a stray wants to gain entrance, he can - just by pushing hard against the cat-flap. The magnetic lock isn't powerful enough to keep out the persistent ones. Back to the drawing board.