Spell Research: Knock and Wizard Lock

The knock spell first appears in original D&D's Book I: Men & Magic. It is a 2nd-level magic-user spell. The description is as follows:

A few things about this are immediately interesting to me. First, the spell opens secret doors, obviating the need to puzzle out how the secret door is intended to be opened. It also means that secret doors which are designed to open from only one side can be opened from the unintended side using this spell. I had always intuited that the purpose of this spell was to unlock doors, not open them, so this is a bit surprising to me on a close read.

I am also surprised to see that knock is a ranged spell. I had always assumed that the magic-user had to physically knock on the door for the magic to work. Since the spell doesn't simply unlock but instead opens such doors, that means doors can be opened at range, allowing any traps triggered by opening the door to be triggered while the magic-user is at a distance.

Interestingly, if we read the spell literally, it does not open doors that are not secret, held, locked by magic, barred, or otherwise secured, so the PCs will still have to risk opening those doors themselves.

No discussion of knock is complete without looking at its counterpart, the other 2nd-level magic-user spell, wizard lock:

Wizard lock has another counterpart alluded to here: hold portal. This post will not cover hold portal because it is not consistently represented in all editions of D&D. It is very similar to wizard lock except that its duration is shorter (think of a magic-user magically warding a dungeon door against an ogre attempting to batter it down, versus a magic-user permanently securing an important door in their inner sanctum).

Knock suppresses wizard lock only temporarily, and does not remove it. The magic-user must cast knock each time they wish to pass through the wizard lock. This makes me want to make the occasional wizard lock door trapped such that it automatically swings shut after a certain number of individuals pass through it, separating the party unless the wizard can open it again.

Interestingly, the magic-user seemingly cannot open their own wizard lock without a knock spell. That seems horribly inconvenient!

Since this is our introduction to the spell, I feel this is a good time to link to Designing Obstacles for OSR Play, which contains some interesting discussion about "Hard Locks" and "Soft Locks" and about knock and the problems posed by "skeleton key" spells like it and dispel magic. The post criticizes the use of wizard lock in published adventures and the tendency of adventure authors to take the ubiquity of knock for granted, rather than including more interesting ways of bypassing wizard lock and related obstacles. I don't see this as being an inherent problem with either spell so much as a flaw in the design culture surrounding these particular obstacles. 

As the post explains, there are much more interesting ways to integrate locked doors and their keys into adventures. The existence and implementation of knock does not offend my sensibilities. If I've designed a truly interesting magically locked door with an ingenious puzzle that needs solving to open it, but the player characters happen to have knock and can bypass it with a single spell, more power to them. It is less interesting, but I'm not always prioritizing what's interesting above all other considerations, such as rewarding players for being well-prepared.

I'm also not entirely sure whether wizard lock would be considered a Hard or Soft Lock. Is it a Hard Lock because it identifies specific means of bypassing it (the implication being that there are no other means of doing so)? Or is it a Soft Lock because there are multiple ways of bypassing it (knock, dispel magic, or the service of a higher-level magic-user)? This issue will only become muddier as we dig into different iterations of the spell.

Another common criticism of knock in particular is that it allows the magic-user to be a better thief than the thief. I will point out that at the time of original D&D's publication, the thief did not exist. The magic-user is not yet stepping on those particular toes. That is about to change.

Knock appears again in AD&D:

This being AD&D, the spell has been complicated quite a bit! It is classified as an alteration spell for the first time. Alteration (later called transmutation) is the school of magic concerned with the alteration of a thing's properties. In this case, the locked object is being magically transmuted into an unlocked object. Sure. That works I guess.

Knock now has an area of effect of 10 square feet/level of the caster. What exactly this means isn't at all made clear. Perhaps it will be clarified in the future, in some sort of updated version of the AD&D rules?

AD&D's version of knock also opens stuck doors (the original D&D version of the spell isn't explicit about this - my interpretation is that it doesn't affect stuck doors, unless a stuck door qualifies as "otherwise secured") and locked or trick-opening boxes or chests (in hindsight, it's interesting that the original spell only works on doors), and loosens shackles or chains. The description also specifies that knock does not open portcullises (the original version's "otherwise secured gates" language may or may not include portcullises). Lastly, each casting of the spell removes only two impediments to opening the door (i.e., a lock and a bar, but not a lock, a bar, and a spell like hold portal or wizard lock).

The thief is now a class. They are pretty bad at the things they're supposed to be good at. Knock, among other spells, allows the magic-user to automatically succeed at the things the thief is supposed to be good at, albeit a limited number of times per day. Similarly, the magic-user also automatically succeeds - again, just a few times a day - at opening stuck doors, which is one of the things the fighter is supposed to be good at. At least the magic-user can't bend bars/lift gates!

I personally am not really bothered by the toe-stepping. The magic-user only has so many spells per day, and if they want to cast knock multiple times they have to use multiple spell slots to prepare it. The magic-user is sacrificing a significant amount of utility just to open the occasional door. There is no on-demand magic (i.e., cantrips) in AD&D like would come in later editions, so the magic-user is making a choice to specialize their loadout for the day and then be limited to throwing their darts or whatever.

I think it's more likely that the party explores the areas of the dungeon that can easily be explored, the fighter and thief try their luck at any stuck or locked doors they come upon, take note of those they can't open, and the magic-user then prepares accordingly for the next delve into the dungeon to open any doors that continue to confound the rest of the party. 

That too comes with tradeoffs. The party may have random encounters as they retreat from the dungeon. If they make camp outside the dungeon - which they would be wise to do - they may have to fend off a dangerous wilderness encounter. While they're gone, the rooms they explored may be reoccupied. They may have more random encounters while traveling back to where the offending doors are. The party can make short excursions into the dungeon to achieve a straightforward goal such as this, but it's simply not an efficient way to explore.

In a world where any magic-user of 3rd-level (which is considered low-level in all versions of the game) can magically open almost any door, you also have to imagine that most important things are going to be behind several secured doors. Or, maybe, just one really secure one.

Each casting of knock only foils two "locks" on a given door. Imagine a huge vault door with multiple complex locking mechanisms and magic wards. The magic-user can get through two at a time. A 3rd-level magic-user can get through two locks per day. At 4th- through 6th-level, they can get through four locks per day. At 7th- through 9th-level they can get through six locks per day. And on and on. Suddenly the thief doesn't seem so superfluous (but you should probably make them more competent somehow - there are far more blog posts on the subject than I care to wrangle right now).

I also like how the spell suppresses a wizard lock for 1 turn specifically. In my world, doors with wizard locks are on a timer - after the turn is up, the door swings closed! I really like the idea of the party breaking into a magic-user's vault with their one use of knock, only to neglect to spike open the door and end up trapped inside.

The AD&D version of wizard lock similarly adds a number of specifications:

Like knock, wizard lock is an alteration spell, has the same unexplained area of effect, and specifies the types of objects it affects. The wizard lock can now be bypassed by breaking the affected object (the Lock is becoming Softer). However, magic-users now need to be one additional level higher than the original caster (i.e., 4 or more levels higher compared to the original spell's 3 or more levels higher).

The bit at the end is referring to the fact that hold portal can be shattered at will by any extra-dimensional creature (demons, devils, elementals, etc.). In other words, wizard lock is a permanent version of hold portal that also effectively keeps out such creatures.

AD&D 2e's version of knock cleans up the 1e version:

First, I love that the spell is now reversible. OD&D and 1e both had reversible spells, but knock wasn't one of them. We don't need a knock spell and a lock spell. They're the same spell. You just flip 'em! 

...Is what I would say, if it weren't for the fact that 2e still has a wizard lock spell! We'll get to that in a moment.

This version of knock makes the odd specification that the spell does not affect "ropes, vines, and the like." Okay. Why would it? It also specifies that the location of a secret door must be known in order for knock to open it. This sounds like common sense to me, but in hindsight one could read the original D&D and 1e descriptions as allowing the spell to open undiscovered secret doors (the 1e version in particular "causes secret doors to open", which is vague wording).

The 2e version also elaborates on the area of effect - delightfully, in my opinion. The intention is, apparently, for more powerful wizards to be able to open larger doors! A 20th-level wizard can knock a 200-square-foot door. How big are a giant's doors? If a standard human-sized door is 4' x 7', a 26-foot-tall storm giant (assuming similar proportions) would use a door that is roughly 15' x 26' (though probably even bigger than this). That would require a 39th-level wizard to open! Does the spell assume the caster is human-sized? Can giant wizards easily knock open their own doors? Much to think about!

2e's version of wizard lock is much the same as 1e's, albeit with an important quality of life change:

The caster can now open their own wizard lock! This feels like it should have always been the case. It also introduces an interesting possibility: If the wizard who originally cast wizard lock is at hand, the party could take the wizard hostage and force them to open all of their locks! I could imagine this happening if the party is raiding the wizard's stronghold and is able to neutralize the wizard, but still needs to gain entry into the vault. The Lock gets Softer yet again!

The description does not clarify the area of effect, but we can intuit that it is similar to knock. Interestingly, a 20th-level wizard can knock a 200-square-foot door, but wizard lock a 600-square-foot door. Such a door would require a 60th-level wizard to knock it open!

So what is the point of the reverse of knock, lock? Well, it only affects doors that have a physical locking mechanism. Because of knock's smaller area of effect, is also affects smaller doors than wizard lock. I have no idea why one would prepare lock rather than wizard lock. Making knock a reversible spell was a good idea, but it ultimately feels like a missed opportunity.

Surprisingly, the 3e version of knock is largely unchanged:

This version specifies that the spell only loosens welds, shackles, or chains which "serve to hold closures shut." I think what it means is that it loosens, for example, chains that block a door or bind a chest, but not shackles restraining an individual. There's a very minor change to its range (most likely accounted for by D&D switching from yards to feet as the standard measurement at the time). Very powerful wizards (and sorcerers) can now unlock very large doors from very far away!

Annoyingly, the description for arcane lock is split onto two pages:

First, the name change. Locking doors with magic isn't just for wizards anymore! Second, it's an abjuration now. This makes sense, as abjuration is the school of warding, protection, and negation. I like it better than magically altering the properties of a door from unlocked to locked. The spell also now requires a material component in the form of gold dust worth 25 gp. 

I like how the spell is integrated into 3e's skill system by specifying that it adds 10 to the normal DC to break open the door or portal. In AD&D, a mundane lock and a wizard lock are equally difficult to force. In 3e, each type of door has its own DC, mundane locks add to the DC, and arcane lock adds onto that, making it possible to create a door that is particularly hard to muscle open.

Importantly, this version no longer allows a higher-level caster to open the arcane lock at will. The Lock has become Harder. 

4e, unsurprisingly, changes knock more than any edition yet:

I don't care for the glowing blue key that floats into the door causing it to glow amber. It's weirdly specific and feels like a video game (a comparison no one has ever made with 4e). Otherwise this is interesting. 

In past editions, knock was a 2nd-level spell, which could be cast by a character of 3rd-level or higher. In 4e, knock is a 4th-level ritual, which means the character must be at least 4th-level to cast it (i.e., it is not comparable in power to a 4th-level spell in other editions). Knock is unlocked (haha) for player characters slightly later in 4e than in other editions.

Since knock is now a ritual, it's not tied to spell slots or to 4e's system of at will/encounter/daily powers. If the party has a knock scroll, they can cast the ritual once. If they have the ritual in a book, they can cast it as much as they want, if they have the necessary components.

This is the first time knock has a component cost. I think this is just because all rituals in 4e have a component cost (have to limit them somehow I suppose - 5e would change this, IMO for the worse). It also makes sense considering that 3e introduced a component cost for arcane lock.

I like the idea of the spell requiring a key carved from bone and etched with arcane symbols (a literal skeleton key) which crumbles into dust after the spell is cast. I suppose the ritual requires a healing surge because it's draining for the caster or their assistants (either can provide the necessary healing surge). I really like 4e's use of healing surges as meta currency and wish 5e did more with its hit dice.

I also like how opening a lock is now a skill check, with multiple locks or closures requiring multiple checks. If the rogue has to do it, the ritual caster should too! The description points to the Thievery skill for its DCs, which are 20 (Heroic tier), 30 (Paragon tier), and 35 (Epic tier). It doesn't seem fair that the ritual caster then gets a bonus to the check, presumably preserving their better-than-the-rogue abilities, but maybe there's something about the math that I'm not accounting for due to my unfamiliarity with 4e.

Knock no longer automatically opens the door, chest, gate, etc.! You still have to physically open the thing. It also destroys an arcane lock, which is too bad. No more automatic door traps.

It's important not to miss what the description is omitting! The range isn't specified (I assume it's roughly equivalent to every other version of the spell). Knock doesn't affect secret or stuck doors or chains anymore. The chains thing always seemed weird to me. The secret doors change is a good one. Players should have to figure out how to open those! Unfortunately, the days of more powerful spellcasters being able to open bigger doors are also at an end.

4e's version of arcane lock is similarly interesting:

Now, the Arcana check of the caster sets the DC to open the lock. This is an elegant solution to the "a wizard X or more levels higher than the the one casting the spell" mechanic. Now, the arcane lock caster sets the DC, and the creature trying to beat the lock has to beat the DC. Simple.

Let's not miss perhaps the most important change: You can now open an arcane lock with Thievery! Rogues and the like are not rendered useless by an arcane lock. The way that I read it is that arcane lock can magically reinforce an existing physical locking mechanism on the door, making it more challenging for a Thievery-using character to open. If the door has no physical locking mechanism and arcane lock is instead simply magically holding the door shut, I don't think Thievery would apply.

In addition, the caster can now designate specific individuals or categories of creatures who can open the door at will. The caster can also set a password, which introduces yet another way to bypass the lock.

In addition to now being destroyed by knock, arcane lock is now also destroyed by a successful Thievery check. The caster also knows instantly when the arcane lock is defeated, meaning it doubles as an alarm spell. That makes it a lot more difficult to break into the wizard's vault.

5e rolls back many of 4e's changes and adds a new spin to the spell:

No longer is knock a ritual. Its range is shorter than ever (unless I'm missing something about the 4e version) - 5e took the 60 yard range from pre-Wizards of the Coast D&D but kept feet as the standard unit of measure from 3e, resulting in a range of 60 feet. The spell once again does not require costly components. It affects any "object that contains a mundane or magical means that prevents access". It affects stuck doors again. It only unlocks one lock at a time. It once more only temporarily suppresses an arcane lock.

The author of the spell saved my favorite change for last. A real juicy sucker punch of a sentence: "When you cast the spell, a loud knock, audible from as far away as 300 feet, emanates from the target object." 

Aside from more powerful spellcasters being able to open bigger doors (no I won't let that one go), this is my favorite change yet. This is the best disincentive to using knock. How badly does the party need to open this thing? Are they willing to alert potentially all of the dungeon's inhabitants? What if those inhabitants come looking for them? They'll have to loot the vault quickly and then make a run for it. Can they use the spell as a diversion? Can they use it to set a trap? Should they cast a silence spell first?

It's fantastic.

The 2024 version of the spell is identical, albeit written more tersely and with Game Terms capitalized according to that style. 

5e's arcane lock preserves some of 4e's changes and blends in a bit of 3e:

You can still designate creatures that can bypass the lock, and you can still set a password. Knock only temporarily suppresses the lock. Instead of setting the DC with a spellcasting check like in 4e, you simply add 10 to the existing DC like in 3e. 5e still allows for the possibility of picking a magically augmented lock. 

The 2024 version doesn't seem to change much:

Unfortunately, you can no longer pick a lock affected by arcane lock. It reads as if you can still destroy the door or force it open, but no guidelines are given for modifying the DC. As seems to often be the case with the 2024 rules, this version offers only (often detrimental) simplification without clarity or innovation.

What's your favorite version of knock? How about wizard/arcane lock? The original versions are short and simple, AD&D's are more complex, 3e doesn't change much, 4e totally reworks both spells, and 5e brings them back to their roots with at least one brand new twist. 

Personally, I like some combination of AD&D's weird specificity, 4e's skill contests with a cost, and 5e's clever complications. There's just one problem that no version of knock has ever solved. The caster should have to physically knock on the door! That really grinds my gears. 

Here's my own version of knock, combining some of my favorite elements from several iterations:

Knock

2nd-level transmutation (ritual)

Casting Time: 1 action

Range: Touch

Target: A stuck door or a door, box, chest, set of manacles, or other closed object secured with a lock, bar, arcane lock, or other means preventing access, with a surface area no larger than 10 square feet x your spellcaster level

Components: V, S, M (a key carved from bone and etched with silver-inlaid arcane symbols worth at least 25 gp, which the spell consumes)

Duration: Instantaneous

Classes: Bard, Sorcerer, Wizard 

 

Make a spellcasting ability check with proficiency against the lock, stuck, or barred door's DC. On a success, a target that is held shut by a mundane lock or that is stuck or barred becomes unlocked, unstuck, or unbarred. If the object has multiple locks, you may continue to make spellcasting ability checks until all locks are unlocked or until you fail.

 

If you choose a target that is held shut with arcane lock, make a spellcasting ability check against the DC set by the caster of arcane lock. On a success, that spell is suppressed for 10 minutes, during which time the target can be opened and shut normally.

 

If you know the mage hand spell, you can use your mage hand to deliver the knock. 

When you cast the spell, a loud knock, audible from as far away as 300 feet, emanates from the target object.

(Written for 5e, but you could easily use it with almost any edition by just changing or omitting certain details.)

The spell is now a ritual, which increases its utility, for better or worse. It has a component cost however, so it isn't necessarily spam-able (not that the 25 gp will be much to player characters for long). The caster has to physically knock on the object (unless they have mage hand, which I thought was a fun twist). We're also bringing back the limitation on the size of the target object, because of course we are. 

Because expert characters like rogues are likely to have expertise with thieves' tools, and the knock spell only grants proficiency on the spellcasting check, rogues are still likely to be better lockpickers than their spellcasting counterparts, but a spellcaster remains a viable substitution if a rogue isn't around. If the target is affected by an arcane lock, it triggers a skill contest, which I feel better represents the different capabilities of more or less powerful spellcasters accounted for in arcane lock's early iterations.

And here is my version of arcane lock:

Arcane Lock

2nd-level abjuration (ritual)

Casting Time: 1 action

Range: Touch

Target: A closed door, window, gate, chest, or other entryway, with a surface area no larger than 10 square feet x your spellcaster level

Components: V, S, M (gold dust worth at least 25 gp, which you use to etch arcane glyphs on the object's surface, and which the spell consumes)

Duration: Until dispelled

Classes: Artificer, Wizard 

The target becomes locked and held fast for the duration. You and the creatures you designate when you cast this spell can open the object normally. You can also set a password that, when spoken within 5 feet of the object, suppresses this spell for 1 minute. Otherwise, it is impassable until it is broken or the spell is dispelled or suppressed. 

When you cast this spell, make a spellcasting ability check with proficiency. The result of your check determines the DC required for a knock spell to suppress your arcane lock.

While affected by this spell, the object is more difficult to break or force open, and any physical locks on it are more difficult to pick. The object's AC increased by 2, and it is treated as one size larger for the purposes of determining its hit points. The DC to force the object open or pick any locks on it increases by 10. If the object's locks are successfully picked, the spell continues to hold the object shut.

As with knock, I made arcane lock a ritual and added the limit on the area of effect (couldn't help myself). I made the arcane lock tougher to physically destroy and clarified that picking the locks still requires the door to be forced. 

In my mind, the spell is both making the lock tougher and physically reinforcing the door. Picking the lock doesn't remove the spell, but it makes forcing the door easier than if you were to try forcing the door with multiple locks in place. Hopefully that makes sense.

And that's knock and wizard/arcane lock! They're two classic spells that have gone through a variety of iterations. I am surprised by both the similarities and differences from one version to another, and delighted by the little intricacies and the ways in which each edition's quirks manifest in the spells' descriptions. They are interesting and iconic spells which are often written off for causing problems, but which I personally feel are just additional magical tools - one most likely to be used by the players to solve problems, and another to be used by the DM to cause them (in a good way).