Knock, as written, takes some of the fun out of the game and some of the utility out of being a rogue. Essentially, it makes Open Lock worthless, as a wand of knock serves as the most effective skeleton key in history. Likewise, its effectiveness is not attested to in the source material; Gandalf could neither unlock nor force open the secret door to enter Moria.
Level: Sorcerer/Wizard 2
Casting Time: 1 round
Target: One door, box, or chest with an area of up to 10 sqft per caster level
Duration: Instantaneous; see text
Saving Throw: None
Spell Resistance: No
The knock spell opens magically or mundanely secured portals and containers. It works on portals that are locked, held, arcane locked, stuck, trick-opening, or barred. It affects secret doors if a secret door is touched.
A hold portal spell is automatically bypassed by knock. Arcane lock is suppressed for 10 minutes if the caster wins an opposed caster level check. Doors that are locked, barred, or stuck may be opened with a caster level check, modified by the caster's spellcasting attribute modifier; the DCs in these cases are the lock DC and the force or break DC, respectively.
Unless the door has been arcane locked, it does not re-secure itself on its own and remains unlocked or unstuck. The spell does not raise barred gates or portcullises, and it will not affect ropes, vines, and the like. The effect is limited by the area. If a door is secured in multiple ways (e.g. locked and barred), a single casting removes only one of those means.
Against barred or stuck doors, knock will always prove useful, as even a third-level wizard will have a higher modifier on average than a raging barbarian (+4 attribute +3 CL = +7 to force, whereas a raging barbarian usually will have a +5). Likewise, the wizard's modifier will increase at a much faster rate.
Rogues and other skill monkeys, however, will always remain favorable compared to the wizard. At third level, a rogue will have 6 ranks, a +3 modifier, and masterwork tools for another +2, for a total Open Lock modifier of +11, versus the wizard's +7. At 10th level, a rogue will have 13 ranks, a +6 modifier, masterwork tools and a +5 item, for a total of +26, versus the wizard's CL 10 + 7 attribute, a total of +17. Likewise, in many cases, the rogue has the advantage of taking 20, whereas the wizard has to simply roll the die and make do with what he has.