I use a single wing clip that attaches to the screen door and locks to the inside door frame. Keeps the cats inside. Should keep a little one inside too!
This is a double one. This style I use has just a single wing. Most any hardware store carries them. If your screen door and outside door lock together, do not lock it from the outside, cause if the door blows closed and locks to the screen door you are not getting back in unless you send someone in through the window! Don't ask how I know. My doors not longer lock together as secure as they once did.
