We've had these doors for quite a while. We have two: one inside the house and one outside attached to the side of the house (the dogs go through a little tunnel, in effect). That's what we call the "air lock." It keeps down any drafts. And wow, they bang throught It! I just gave the re-order info to my spouse so we can replace one of the doors. Our experience has been similar to others: very nice door, but the bottom magnetic strip breaks off, and you have to buy a whole new door. Also, it would be good if it didn't come packaged with those annoying styrofoam peanuts (at least ours came that way).