Does Magic Mouth require a line of sight between the object and the trigger?

Question

The magic mouth spell plays a message that is uttered when a trigger condition is met, and states:

The triggering circumstance can be as general or as detailed as you like, though it must be based on visual or audible conditions that occur within 30 feet of the object.

In previous editions, it specified that line of sight was required to activate, but in 5e it doesn't. Does this mean that a magic mouth can activate based on things that are not invisible, but without direct line of sight to the object, such as a goblin behind a wall?

Answer 1

No, it doesn't require line of sight to the triggering entity

The triggering circumstance can be as detailed as you like, though it must be based on visual or audible conditions that occur within 30 feet of the object.

Since line of sight isn't specified, we can't assume it's a constraint on the spell. Line of sight is only required when targeting creatures and objects and when the spell specifies line of sight. As long as the visual circumstances can be seen from that object's vantage point. Thus, if the trigger can be seen or heard from behind a wall, it can be triggered. Auditory cues are the most obvious choice here. Other cues might be shadows cast by a creature.

Some examples that might help

• Trigger when a creature is heard
• Trigger when the door is opened while in a dark room (assuming light would pour in)
• Trigger when a secret word is used
• Trigger when the shadow of a creature is seen from behind a wall

Remember that the condition you specify must be met in some capacity, so be as specific as you need or as vague as you need.