Pet Doors for Glass
For a detailed comparison of the different through glass pet doors, click here to read a blog post on the subject.
These glass dog doors can be installed in windows and sliding glass and French doors. By replacing the glass in your french door, you can install the Hale In Glass pet door or the Pet Door Guys replacement window. With the Hale you just get a pet door and the piece that fits into the corner of the door frame to connect the pet door. It's cheaper up front, but by the time you get the glass work done it will almost always be more expensive than the Pet Door Guys option. The Pet Door Guys product is a complete new window unit complete with its own frame, a tall window on top, smaller one on the bottom on one side, and the pet door on the other side. Just take the old glass out, and install the new glass with the pet door in it. The Hale is the better looking and more expensive option. The Pet Door Guys is cheaper and easier to install.
The downside to the Pet Door Guys is that it has two separate insulated glass units and a T frame in the bottom that separates the top window from the bottom window and pet door, which is less