Can the spell Arcane Lock be used on objects like books or backpacks?

Question

Having recently had to endure a nosy little halfling, my wizard is considering going ham with Arcane Lock. The spell states that casting it locks

a closed door, window, gate, chest, or other entryway, and it becomes locked for the duration.

Obviously, neither a book nor a backpack are an 'entryway', but neither is a chest. There are plenty of books (many modern day diaries or journals, for example) that come with a locking cover, and it makes sense to me that this spell would affect the lock of such a book. But what about an item without a built-in locking mechanism?

The spell description refers to the target of the spell as an object on several occasions. Since a book is a closeable object, would Arcane Lock work to lock the book shut? How about a belt pouch, or backpack?

Answer 1

Up to your DM

This is one of those edge cases where the DM needs to adjudicate.

However, whether it should work for a book with a lock (like a modern diary, as you pointed out), or a book without such a locking mechanism, going by the examples the spell does give, I'm not sure what I would rule on this.

The spell says (PHB, p. 215):

a closed door, window, gate, chest, or other entryway ...

At least most of these are things that have locks on them, or at least can have locks on them. A book can have a lock on it (i.e. the locked diary), so then the question becomes "does arcane lock lock things that can have locks on them, but don't?"

The spell also says:

While affected by this spell, the object is more difficult to break or force open; the DC to break it or pick any locks on it increases by 10.

It says "to break it or pick any locks on it". This, to me, suggests that the objects should have a lock, since this seems to have been worded with a locked door in mind. Those are the two main ways to get past a locked door. Under this interpretation, a DM could rule that you can cast arcane lock on a book with a lock already on it, but not a book without a lock.

However, the fact that it says "or", could equally be taken to mean "if it has a lock, you can pick the lock, but if not, you'd have to break it", meaning that the door, window, etc, doesn't need to have a lock on it to be a valid target of arcane lock. But then, what stops this spell from targeting any object? Already we have an inconsistent list with "chest, or other entryway"...

So we're still left with "up to the DM". If the DM did allow it, then if someone wants to open your arcane locked book, they'd need to either pick the lock, or break it open (with great difficulty) to see the pages inside. This would, of course, be the same for any such item the DM ruled would be valid (backpacks, etc).

Answer 2

As a DM I'd rule yes, RAW is unclear what an entryway is.

You touch a closed door, window, gate, chest, or other entryway, and it becomes locked for the duration.

So we have our examples and a few things to pay attention to RAW

1) You are touching the object, not a lock

The magic is the lock, if it required a lock it would say so in the spell text.

2) In the following description, it specifically states that the object OR the lock on the object become harder to open [emphasis mine].

While affected by this spell, the object is more difficult to break or force open; the DC to break it or pick any locks on it increases by 10.

3) The ambiguity is on an entryway, but if a chest counts, a book would almost certainly also count

Granted if no lock is on the book already you're looking at a book with a DC 10, there are knots in 5e Mike Mearls on Knots which means there are ways to secure even a mundane bag and make it hard to open, thus Arcane lock would be useful there.

Answer 3

If the book has no lock, as a DM I would rule "no".

But, as you said, there are many examples of books with locks - both in modern book shops and fantasy literature or movies. I don't see it inconcievable for a spellcaster to have a book with a mechanical lock on it (or even a simple latch), in which case there would be a "entryway" into the book.

And if all else fails, you could always buy a simple box with a lock and put your book in there.

Answer 4

RAW, no

In DnD 5e, spells only do what they says they do. You correctly quote what the spell locks:

You touch a closed door, window, gate, chest, or other entryway, and it becomes locked for the duration.

A lockable book and other object is not included in the list of objects affected by this spell, so this spell won't work.

However, your DM can choose to allow this. If I were the DM, I think having a lock is a reasonable argument, thus I will allow the spell to work.

Answer 5

I would say yes. Then apply a little logic.

Let's say that even a strength 1 character can force open a book. As such a book without a lock has a DC of -4 to force open, even a str 1 character almost always opens it.

Now take the part of the spell description that says add 10 to the DC to force open. If you cast the spell on that book, it now has a DC of 6 to open.

I would also give the halfling penalties based on how careful they are trying to be. The halfling wouldn't want to use it's full strength, but maybe they do (and risk damaging the book). So that put's a bit of decision making and roleplaying into the hafling's efforts.

Answer 6

From an in-universe standpoint, I would rule a definite No to the backpack, and most likely a No for the book.

The reason is that I imagine this spell to basically harden the door and connect it to its frame such that it's no longer as easily moved, preventing people from just kicking it in. Similarly, the lock's gears would similarly be so heavy that the locksmith's tools have trouble moving them, so the Lockpicking DC increases.

If you were to try the same for a book or a backpack, the result would be strange because the object itself is small, mobile, and sort of lacks a frame to Lock the moving bits to. There would be the question of whether you could move the book in its entirety at all any more, or if it would resist an attempt to be carried as well. An a leather backpack would stop feeling like leather because the hardening part of the spell would have to affect the entire thing.

Therefore, based on how a GM rules on how to interpret the "chest" bit of the spell description, the book might or might now be applicable: If it's meant for large, assumed to be immobile chests like treasure chests in a dungeon (which people will rarely try to drag anywhere), then it would be a No for the book. But if the GM allows people to carry a Locked chest, then a Locked book would make some sense as well. It would basically be a wood pulp brick because the individual components can't be moved against each other any more.