The knock spell opens stuck, barred, locked, held, or wizard-locked doors. It opens secret doors, as well as locked or trick-opening boxes or chests. It also loosens welds, shackles, or chains. If used to open a wizard-locked door, the spell does not remove the former spell, but simply suspends its functioning for one turn. In all other cases, it permanently opens locks or welds—although the former could be closed and locked again later. It does not raise barred gates or similar impediments (such as a portcullis), nor does it affect ropes, vines, and the like. Note that the effect is limited by the area; a 3rd-level wizard can cast a knock spell on a door of 30 square feet or less (for example, a standard 4-ft. x 7-ft. door). Each spell can undo up to two means of preventing egress through a portal. Thus if a door is locked, barred, and held, or triple locked, opening it requires two knock spells. In all cases, the location of the door or item must be known—the spell cannot be used against a wall in hopes of discovering a secret door.
Lock[]
The reverse spell, lock, closes and locks a door or similar closure, provided there is a physical mechanism. It does not create a weld, but it locks physically operated locking mechanisms, set bars, and so on, up to two functions. It cannot affect a portcullis.