Does Enthrall make targets require perception checks to perceive anything other than the caster?

Question

From the description of the enthrall spell (emphasis mine):

You weave a distracting string of words, causing creatures of your choice that you can see within range and that can hear you to make a Wisdom saving throw. [...] On a failed save, the target has disadvantage on Wisdom (Perception) checks made to perceive any creature other than you until the spell ends or until the target can no longer hear you. The spell ends if you are Incapacitated or can no longer speak.

Our group is divided on the how this should affect situations that wouldn't normally require a perception check (e.g. someone coming up to talk to the affected character). Here are the possibilities we came up with:

1. Things that would normally not require perception checks now do, and such rolls are made with disadvantage.

2. Things that would normally not require perception checks still don't.

An Internet search hasn't turned up anything on this specifically.

Answer 1

It affects passive perception

Page 175 of the PHB tells us that if you have Disadvantage on a check, your passive check total (aka. score) is lowered by 5.

Things you notice automatically can be treated as having a low enough DC to spot that most creatures will beat it with their passive perception. You normally do not deal with events or objects that are DC 6 to spot as even low-wisdom creatures have a passive score of 9, maybe 8. But give a creature with a passive perception score of 10 (average for a human) Disadvantage and their score will drop to 5, making them miss a DC 6 phenomenon.

Whether to call for an "active" check after a fail with the passive score or not (meaning the creature does not notice the thing at all) is another question and the DM will have to make a ruling on it based on the circumstances, as always.

Answer 2

Things that would normally not require perception checks still don't

The creature affected by the spell is very distracted, but still has its wits about it. This is why they have advantage on the save whilst in combat, because they are already alerted to a combat situation and are less easily distracted.

I believe the intent here is that you could enthrall the target, and take its full attention while someone tries to sneak past it (imagine a gate guard). They couldn't easily listen or look for other creatures whilst hearing the casters 'distracting string of words' and concentrating on that.

If however someone walked up to the affected party and tried to strike up a conversation, a distraction would not be enough for them to have difficulty seeing them.