D&D 5E Magic Mouth visual trigger & invisibility

[5ekyu]

Noise, sure, the magic mouth could trigger on that.

But hostility? Intent isn't part of the spell.

If the magic mouth could discern intent, it would jump from niche use to one of the most potent spells in the game!

Yeah, I pretty much take the dpell at fade value. I dont divine out of it any infallible hearing or microscopic sight or any of that. I just use very basic perception rules like it was a creature.

If it's hot clear line of sight to a non-invisible entity, it sees it. If it's not moving dilrnyly, it hears it. It can be fooled by disguises. Etc.

If someone wanted to "imbed extra senses" sure but I would likely handle that as a ruling requiring the MM be cant using higher level slots to cover the additional senses. But then, maybe not. After all, if I can turn magic mouth into a "one use until triggered" alwsys on invisible detection or truesight - that has pushed it way beyond its already powerful limits. So, I would only let the embed last for the duration of the embed, not the full run of the magic mouth.

 

[Oofta]

The spell states that it must be based on visual or audible conditions that occur within 30 feet of the object. So it partly depends on what the criteria is. In general audible conditions in my ruling have been the magic mouth responding to the spoken word or other obvious audio cues like ringing a doorbell.

Magic mouth is not intelligent per se, it doesn't have any special modes of sight, it has somewhat limited ability to interpret what's happening. Even if it's triggered off any sound, the person entering the area could always make a stealth check to move quietly.