The old study screen door was actually a storm door that we didn't have a screen for. We had intentions of putting a full screen door in its place, since you don't really need a storm door in Austin. But then we started letting our cat go outside. Then she sat at the by the door and meowed. All the time.
So instead we took off the storm door and fixed the old, broken doggy door (or in this case, kitty door) in the main study door. So now Pip (the cat) can come and go as she pleases.