The 4-Way Locking Cat Door allows you to control your cat's access in and out of your home. The 4-Way lock allows you to choose from four access options: open, locked, in-only and out-only. The open option allows entry or exit, the locked option does not allow entry or exit, the in-only option allows entry but no exit and the out-only option allows exit but no entry. The 4-Way Locking Cat Door can be installed in interior or exterior doors or walls. An optional tunnel is included for installation in doors and walls 5 cm (2") thick. Additional tunnels are available (sold separately) for installation in doors and walls thicker than 5 cm (2"). For installation help and tips, view the installation video below.