A privacy knob is typically used on bathroom or bedroom doors. It features a push-button or turning mechanism on the inside to lock the door, but it can be opened from the outside in an emergency using a special key or tool. A passage knob, on the other hand, is used for doors that don't need a lock, such as those to a cupboard or hallway. It simply has a latch that holds the door closed, and both knobs turn freely.