If youre installing a SmartDoor Connected Pet Door in metal, glass, or a wall, then youll need this SmartDoor Installation Adaptor. The adaptor minimizes the interference that may occur between a metal door, your pets door key and the sensor that gives them access through the SmartDoor. This installation adaptor will help secure your new pet door in a safe manner by giving you something to screw into. Some installation locations require additional PetSafe accessories or professional help. The installation adaptor comes in two sizes, Medium and Large, and must match the size of your existing SmartDoor. Please note that only the Medium SmartDoor can be installed in glass. Consult a glazier for glass installations. This product is only compatible with the app-enabled SmartDoor Connected Pet Door.