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 2" thick. Additional tunnels are available (sold separately) for installation in doors and walls thicker than 2".