A while back there was a thread about pet doors and I posted a response about the one I had in our sliding glass door before we replaced it with french doors. I've not seen these anywhere since ordering mine (about 15 years ago) and just came across some. Thought I would share in case anyone is interested...
http://www.akcstore.org/akcstore/Pro...roductID=52462
I'm sure you can find these elsewhere also... just wanted to share a picture so you could see what it is.