Do auras require line of effect?

Question

Several in-game effects, such as all the paladin's auras (PHB p. 85) and spells like Aura of Life and Aura of Purity (PHB p. 216), are passive auras that radiate from the point of origin (usually a creature). The descriptions contain language similar to:

… each non-hostile creature in the aura (including you) …

or

… you and friendly creatures within x feet of you …

Do these auras affect creatures who are within the range of the aura, but behind total cover?

Example 1: A paladin stands with their back against a wall. On the other side of the wall is an ally who is within 10 feet but behind total cover. Does this ally get the paladin's Charisma modifier added to their saving throws because of Aura of Protection?

Example 2: A magic item has the following property:

While within 30 feet of the [magic item], a creature is under the effect of a protection from evil and good spell …

This magic item is small enough to be placed in a chest; doing so puts it behind total cover. Do creatures within 30 feet of the chest still benefit from the effect of the aura?

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Based on these examples, it would make intuitive sense for auras to require line of effect, but I am having trouble finding explicit support for this in the rules as written. Applying the rules for Areas of Effect (PHB p. 104) would mean total cover blocks auras, but are these rules applicable to non-spell class features, such as the paladin's auras?

Answer 1

Rules as written, no, auras don't require line of effect.

There is a general rule, regarding the area targeted by spells, on page 204 of the PHB:

A spell's effect expands in straight lines from the point of origin. If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn't included in the spell's area. To block one of these imaginary lines, an obstruction must provide total cover, as explained in chapter 9.

However, many auras are not spells - and even spells that cause auras do not have an "area" parameter described as an aura - there is no such thing. The target of these spells is typically a single creature or object that is invested with the aura, which is then described separately in the spell's description; the aura is not subject to the area rules which define who is targeted by a spell, and the creatures who may end up affected by an aura are not the spell's targets.

An "aura" seems to be an entirely separate concept which is not specially defined anywhere else. Thus there are no general rules describing how auras work and certainly no rule that states auras require line of effect, so the effect of an aura is only blocked by cover if the description of the aura states it is. Usually, the only criteria given is that the subject is within a certain distance of the aura's source, and there is no mention of any obstacles that might be between them - though there are many auras that specify that the subject must be able to see/look at the source of the aura as well, so line of sight is necessarily required in those cases.

The Antipathy (Sympathy) spell is a particularly unusual case which specifies an aura which takes effect if the creature is within 60ft of the source or can see it, giving it an astonishingly large effective range (and suggesting that line of sight is not at all required for the effect if you're within the 60ft radius).

DM discretion obviously applies.

Any given DM, of course, is free to rule differently. The spellcasting system establishes that line of effect is required as a general rule when targeting spells and affecting areas, so it's not wildly unreasonable to decide that other supernatural effects are subject to similar restrictions. Personally, if it came up, I would be tempted to houserule that the same rules that Detect X spells impose on their ability to detect "auras" apply to the propagation of other auras:

The spell can penetrate most barriers, but it is blocked by 1 foot of stone, 1 inch of common metal, a thin sheet of lead, or 3 feet of wood or dirt.

This makes for a more interesting tactical experience as regards positioning - wooden or shallow dirt walls would not usually offer any cover from an hostile aura or impede benefiting from a friendly one, but stone or metal walls would.

Answer 2

I don't think there is an absolute explicit answer in the rules so it's up to the referee.

Radiates means emit as rays or waves.
If this was light then it would hit a door and you can't detect the nasty stood on the other side.
Light does not penetrate doors.
On the other hand, this is not light, it's something else.

Even if you apply a literal meaning to that word it is still going to penetrate objects and detect that nasty on the other side of a door or round a corner.
Like a sort of evil x-ray detector.

Should it really be blocked by anything blocks LoS?
Your paladin can only detect evil if he sees them? Do you need to arrange the party so there's a direct line of sight between each and the Paladin?

That seems an unlikely intent to me.
My inclination is that this is intended to just work as a radius and you ignore things intervening.
Unless maybe these are magic nullifying barriers of some sort.

"I've got a bad feeling about whatever is on the other side of the door".
That seems much more like it than. "Sorry, can't sense anything. That tent canvas is blocking the vibes".

Answer 3

I would say Auras do not need Line of Sight

As you say, it does not seem that there is anything in the rules regarding auras needing line of effect to work, whereas for spells this is specifically stated. Without such a specific rule I would say that line of effect is not needed for auras.

This is slightly supported by the following tweet from Jeremy Crawford:

Identical spells don't stack (PH, 205), but nothing stops the auras from stacking. Could always house rule it.

While not covering the same question, it does show that auras should be treated diferently from spells.

Hope that helps!

Answer 4

There is no explicit rule for auras; however we can make a reasonable assumption based on what it is not.

A line of effect is necessary for things that are physical. ie an arrow, the effects of fireball or burning hands, magic missiles, etc.

A line of sight is necessary for things based on vision. These effects usually have the phrase "that you can see" in the descriptions. ie petrifying gaze, horrific visage, targeting non-physical spells, etc. For example, the lich's frightful aura reads (emphasis mine):

Liches are shrouded in a dreadful aura of death and evil. Creatures of less than 5 HD in a 60-foot radius that look at the lich must succeed on a Will save or be affected as though by a fear spell from a sorcerer of the lich’s level.

And the bane Spell:

Up to three creatures of your choice that you can see within range must make Charisma saving throws. Whenever a target that fails this saving throw makes an attack roll or a saving throw before the spell ends, the target must roll a d4 and subtract the number rolled from the attack roll or saving throw.

An aura is an ethereal manifestation not a physical one, and nothing in the description defines that you need to see. So neither line of effect nor line of sight applies.

The spell detect magic does specify:

The spell can penetrate most barriers, but it is blocked by 1 foot of stone, 1 inch of common metal, a thin sheet of lead, or 3 feet of wood or dirt.

Since detect magic detects magical auras, it would be reasonable to say that the paladin's auras have the same limitation.