Amazon.com: PetSafe Interior Cat Door: 2-Way Locking, Indoor Pet Door Flap - Tinted Privacy Door for Cat Litter Box or Pet Feeder, Built-In Door Lock, Durable Door Frame, DIY Easy Install, Hardware
A Homemade Pet Door – Mother Earth News
Pet Door Window Insert From XPS Foam and Double-Pane Glass : 8 Steps (with Pictures) - Instructables