Does Arcane Eye require Stealth checks to avoid being discovered?

Question

TL;DR: DM keeps calling for Stealth checks for Arcane Eye claiming it can 'be run into by creatures' or 'bump into things and accidentally make noise'. Correct or incorrect?

Long version: My DM really doesn't like Arcane Eye. He feels that it 'ruins the suspense' of dungeon crawling. At one point he tried to nerf it to 10 minutes instead of 1 hour but I got him to back down on it. One concession I have let him make is that the doors in the Princes of the Apocalypse dungeons don't have an opening 1 inch or more, which is fine, so I can't scout the entire dungeon in most cases. That's fair. But since then he's been calling for Stealth checks with Advantage pretty frequently for the Eye. When one of the monsters eventually succeeds he has them attack it without allowing any reaction on my part or entering rounds, it just 'suddenly disappears'. As far as I can tell, unless something can see Invisible creatures through some means, they shouldn't even get a Perception check to notice it. It flies, so it leaves no tracks. It's literally just eyeball, so it cannot make any noise.

I went so far as breaking down the Invisible > Heavily Obscured > Blinded connection for him. As far as I can tell he is objectively wrong and is trying to nerf the spell because he doesn't like it. What say you?

Answer 1

Arcane Eye creates a spell effect, not a creature, nor an object. Only creatures make Dexterity checks. If the eye is detected by something like a creature with truesight, the eye cannot be damaged any more than one could damage a fireball or magic missile, but it could be dispelled.

Answer 2

As Derek's answer already addressed, there's no reason for the Arcane Eye to make Stealth Checks (because RAW it does not physically interact with creatures), or for it to be attackable. RAW, the only way to eliminate the eye is to disrupt the spellcaster's concentration (usually by attacking them directly) or causing an effect that disrupts the spell itself, like Dispel Magic.

But let's ignore that for now. Let's just assume that, for the sake of your campaign, your DM has specifically chosen to houserule that the Arcane Eye is its own creature, completely controlled by the caster, existing for the duration of the spell, with stats and movement as though it is a floating eyeball that has the ability to fly 30' per round and is innately invisible, thus requiring stealth checks to go undetected.

Your DM is handling Stealth checks incorrectly.

In multiple ways.

You're rolling the Stealth check itself incorrectly.

First off, being invisible doesn't confer advantage to Stealth checks. There are lots of mechanical implications of Invisiblity on a Hidden creature, but advantage to Stealth Checks isn't one of them.

Additionally, you should only be rolling Stealth once, when the creature takes the Hide action. Rolling more than once nearly guarantees a creature will fail their attempts to sneak past another creature, and makes the ability nearly useless. If they are discovered, they may attempt to Hide again, making another stealth check, but of course, by that point, their presence will already have been alerted to, making the situation already more difficult. And for a non-invisible creature, they may not have cover to Hide behind.

One thing Invisibility does, however, is confer Disadvantage to the perception checks of creatures (without Truesight) that attempt to perceive it. Granted, this is true of most perception checks for hidden creatures, because most of the conditions for Hiding require some degree of vision obscurement. Regardless, on a passive Perception roll made with Disadvantage, this is mechanically implemented as a flat -5 penalty to their passive Perception score.

Speaking of...

Perception is being handled incorrectly

There are specific scenarios where a perception check should be used with respect to a hidden creature. Whether said creature is Invisible or not is completely irrelevant, what matters only that they are Hidden, which does not require a creature to be invisible, it only requires they be behind cover, or in an obscured area, the latter of which being what the Invisibility condition provides.

These are the three scenarios where Perception (in relation to hidden creatures) is meant to be used

1. A creature is hidden, and other creatures not already aware of the creature are in its vicinity. The creatures unaware of the creature make a Passive Perception check (no dice are rolled; result is 10 + their Perception Modifier), with a successful check allowing them to know the position of the hidden creature.
2. A creature is hidden, and other creatures are (or are not) aware of the creature, and make an active effort to search for it. This is represented by the Search action found in the "Actions in Combat" section of the Player's Handbook. They then make a regular Perception check (d20 + their Perception modifier). This check will usually be made with Disadvantage, since most mechanisms that enable hiding confer disadvantage, like Cover, or obscured vision (poor lighting or fog) or invisibility.
3. A specific spell or class feature or racial feature specifically calls for a Perception Check.

Short of that, creatures should not be making active perception checks if they're not already consciously aware of the creature OR not making an active effort to Search for it.

Taking all of this into consideration

So if we still ignore the parts about Arcane Eye not actually summoning a physical creature, and presume it's necessary to handle stealth at all for it, here's what should be happening.

1. When you first summon the Arcane Eye, it should be assumed (or explicitly accounted for) to be attempting to Hide. You'll make a Stealth roll for it, using whatever modifier the DM thinks is appropriate for a tiny floating eyeball (I'd use your Spellcasting Modifier + Proficiency, but that's just me)
   • Some DMs prefer to roll the stealth check in secret, rolled by them, and the number not revealed to the player who ostensibly made the check, in order to prevent metagaming. There are arguments for and against this practice, which are out of scope for this answer, except to acknowledge that your DM may choose to do this.
2. This Stealth Roll will persist until such a time that the eye is discovered (if at all).
3. When the eye enters the presence of another creature, if that creature has Truesight, the eye is seen, its hiding is pointless, and the eye cannot hide unless it goes behind cover.
4. Otherwise, the creature's Passive Perception (10 + Perception Modifier - 5 for the Disadvantage) is compared to the Stealth roll you previously made. If it is below the stealth roll, they are unaware of the eye, and the eye can sneak past them without risking getting caught.
5. If the perception check passes, they become aware of the eye's position, and the eye is no longer hidden. The position of the eye remains known to the creature (and any creatures they inform) until (and only until) the eye attempts to Hide again. At that time, you will make another Stealth check (same as before)
   • Sidebar: this is usually the point where a DM would call for an initiative roll between the eye and the creatures it is trying to sneak past. You generally would not call for initiative at any point before this moment unless a creature had Truesight, or you were already in combat before this business began.
6. Once again, you compare against the Passive Perception checks of these creatures. Same rules apply
7. However, they are now "aware" of the eye's presence, which means they can now start making Active Perception checks (made with Disadvantage) using their Search action each turn to try to locate the eye, in addition to their passive perception scores
8. This continues until you leave their vicinity or until they destroy the eye

So when handling stealth in the future, use these points as a guide for working out how it would impact your use of your DM's altered Arcane Eye spell, or for other uses of Stealth in your campaign in general.

Answer 3

Your DM is wrong

tl;dr/mathless: The Eye is Invisible and under an inch in diameter; much too small for an enemy firing blindly to even hope to hit, and too small to make any noticeable noise without smacking into an object at speeds much higher than it can attain normally.

Also, the RAI and RAW is that it can't be attacked, because it doesn't have stats or Hitpoints. The scenario your DM is proposing is extremely far-fetched, bordering on ludicrous.

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For the purposes of being complete, I will make this much harder than it needs to be

Arcane Eye creates a "Magical Floating Eye" that hovers above the ground and can see 30 Feet in any direction, even in the dark. It is not said whether it is intangible or not, but text within the spell would suggest that it is, in fact, tangible.

A solid barrier blocks the eye's Movement, but the eye can pass through an opening as small as 1 inch in diameter.

The Eye has enough of a physical presence to not be able to move through a solid object, or any hole smaller than one inch.

However,

it's still really tiny. Creatures can, in-general, fit through a hole of their size category, or one lower if they squeeze (PHB 192). The Eye does not have to squeeze to fit through that inch (inferred from the fact that it loses no additional movement when doing so, unlike squeezing, which uses twice movement).

That means the Eye, which cannot squeeze, is just under one inch in diameter (it "creates an eye", and eyes are roughly-spherical), because it cannot pass through any hole smaller than an inch in diameter, but can pass through any size larger hole. This would give it an approximate volume of: $$4/3π r^3$$ $$4/3π * 0.5^3 ≈ 0.52cu.in$$

By comparison, the smallest Size Category in D&D 5e, Tiny, occupies a space of ~2.5x2.5ft (or 30x30in) cube, meaning it has a volume of: $$30^3 = 27,000 cu. in$$

Your Arcane Eye is ~2*10^(-5) times as large as the Tiny size category

This absolutely miniscule size, coupled with the fact that it is invisible and floating, would mean that even if a creature managed to detect it somehow without relying on sight, the eye is almost impossible to hit. That's not "Attack at Disadvantage," difficulty that's "Attack at Disadvantage, only a Natural 20 on the lowest die Hits" difficulty.

It also means that it is incredibly improbable that a creature will somehow blunder into the eye without your eye being able to dodge it (since all actions happen simultaneously). The eye can go through an opening of one inch, and there are usually several inches between most humanoid's legs (Of course, there are always Gelatinous Cubes.)

And this is even if it were possible to attack it, since it has no stats, no AC, and no Hitpoints.