It has a slide-in closing panel with a lock so you can restrict access when you don’t want your cats going out, and the whole thing is easily removed thanks to its spring-loaded frame that lets you lift it right out of the sliding door track.
Promising review: “Our cats took right to it! I figured it was going to be a nightmare training them. One of them jumped through it as I was installing it, AND I even had the main door wide open. It was hilarious! Anyway, I wanted to say that the retractable top makes it so easy to install and remove at will! It wasn’t something I was looking for, but once I realized this awesome feature, I knew it was a bonus! So, I quit on installing it permanently with all the screws and went with it as is. Now, when we are going to be gone longer than a day, I can just simply pull the retractable top down a little and remove the door. I was a little bummed about the sealing, or lack thereof, where the door makes contact with the PetSafe insert. So, I just ran up to the store and grabbed a couple of different weather strip seals and put one on the PetSafe insert and one on our sliding glass door, overlapping them so they seal each other as the door closes shut. We bought the medium-size pet door because we have 15- and 20-pound beast cats. Our biggest fits just fine. I also fashioned a bar to fit between the door to brace lock it when we are asleep or gone. Lastly, the weather stripping it came with for the back of the door is fantastic! Very simple, and the sticky stuff is great!” —Lookin4That1Thing
Get it from Amazon for $179.95+ (available in two colors, five sizes, and four styles).