Magic Mouth - conditions?

[MarkB]

One simple idea I had for the Magic Mouth ritual was a simple Alarm spell. Basically, I get a small carved figurine of a dog, cast Magic Mouth on its mouth, and specify that, when the figurine is stood up uncovered, if any humanoid or large creature other than those present when it was set in place approaches within fifty feet, it should immediately cry out "Awake! Fear! Fire! Foes! Awake!" loudly enough to awaken nearby sleepers.

A simple enough set of conditions (though perhaps I would need to specify the 'friendlies' at the time of casting), but how reliably will it work in practice? Can the Mouth tell automatically if a creature of the specified type is present, making it a perfect watchdog? Or does it have a Perception skill, perhaps equal to that of the caster at the time it was created? Or will it only react to a creature that can be clearly 'seen' without any obstruction?

I'm guessing these are questions that individual DMs must answer for their own campaigns, but wondered if anyone had found more concrete answers.

 

[Dalzig]

You're absoluetely right that it's up to the DM.

I'd rule that any condition set will work, unless someone is purposefully denying that condition. Then, it only has a chance of working.

For example, a devil of somekind uses a ritual to completely disguise itself as a human. If the magic mouth is set to go off when a devil shows up, it will get about a 50/50 chance to work, depending on level difference, etc. etc.