Are you installing your SmartDoor Connected Pet Door in a thick door or wall? These SmartDoor Tunnel Extensions will give your pet a safe and clear path through. Each extension adds 5 cm to the overall depth of the tunnel between the SmartDoor and your pet’s destination. Tunnel installation is quick and easy, requiring no tools. Simply glue or tape the extensions in place. Be sure to add enough extensions so that the final piece sticks out of the door or wall by at least 3 cm. The extension tunnel is needed for installation in metal doors thicker than 4.4 cm, non-metal doors thicker than 5.7 cm in and wall installations. Tunnel extensions come in 2 sizes, Medium and Large – be sure to purchase the size that matches your SmartDoor. This product is only compatible with the app-enabled SmartDoor Connected Pet Door. Your pet deserves the best. Trust PetSafe® to keep your pet healthy, safe and happy.