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?
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?
Best Answer
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:
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:
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.