Door knobs are available in a variety of finishes, it is an easy way update existing doors no matter what style you select. For security purposes, keyed door knobs should be placed on all exterior doors. Privacy door knobs lock from the inside and are most commonly used for bathrooms. Passage door knobs have a latch, but they do not lock. Dummy door knobs are used for French doors or doors that do not require a latch and are a great way to update existing doors. Just be sure the style you select is consistent throughout the room.