I realized that since this spell can be triggered multiple times until it's dispelled you could totally make walls have a conversation with its self any time someone enters a hallway.

"Hey, what're THEY doing here?"

"Don't know but they're UUUUGGGGGLLLLLLYYY,"

and so on.

In the last paragraph it states that "the triggering circumstance can be as general or as detailed as you like, though it must be based on visual or audible conditions..." 

Is that an exclusive "or," or could the trigger be "when someone is holding up two fingers and says the secret code?" I've thought it is exclusive but it looks like it works with both. In its own example, "when a silver bell rings within 30 feet of it" seems like a visual and audible observation. You could argue that it knows the frequency differences of the bells and that's fine, but using multiple of these together could be useful in the event of some of them triggering others, but the second ones to trigger need both a first mouth active and also a visual trigger. 

2.5-year late edit: "conditions" not "contitions"

I'm wondering if you can have multiple concurrent instances of this spell on the same object. The rules do not state one way or another.

Basically I want to know if I can use this to make a magical Billy Bass.

I've come up with a number of lovely uses for this spell, but my favourite so far is enchanting a statue of a god to speak to its followers!

There's no described limit on how many times the spell can be cast on a single object, so over time you could string together hundreds of these things to all trigger after the previous one finishes speaking. You could macro the statue to say whatever you want if you've got time and enough creativity. Even a one time application of 25 words could do a lot of moral damage or lead to greater physical damage via friendly-fire if the dice roll well.

Is this a typing class word per word count on most digital programs or a word as in any word found in a dictionary?  It would make quite a difference between the 1 word count of "supercalifragilisticexpialidous"  vs.

"super   cali   fragil  listic   expi   ali   dos   ious,"  Don't know if Wizards has expounded on this or if it's another "DM discretion" area of the game.

Interesting that the object must not be carried at the time of casting, but it says nothing about wearing or wielding it afterwards...

So if you wanted, could you use a spell that makes sounds that can hurt people (like Vicious Mockery or Shatter) as the "message?" Like when you are supposed to say something can you just cast one of those spells and use it as the message?

You would not be able to get multiple castings of a spell or cantrip just by recording the verbal component (and keep in mind that Shatter also has Material and Somatic components).  Accessing the Weave requires intent and manipulation from a caster, otherwise we'd sometimes get random spell castings just from the wind howling in just the right manner.

Oh ok that's a fair point. I was just curious if that was possible

I'd say "no" since spells are more than just words.  They're also, at least intent and willpower.  This spell confers neither of those.  That said, there are wards/glyphs for your desired purpose ;)

Alright, thanks for letting me know!

Word count, not syllable count

I have a question. Say I set up over twenty of this spell. Each with a trigger to say "There are now X number of people in the room." With the trigger being when that number of people first enter the room. Would that bypass stealth if someone was hiding. What if someone was invisible? Or change the trigger to be 'When the number of people observing the room becomes X then...' would that qualify if divination sensors appeared in that room? Could I set the magic mouth to speak whenever X number of poisoned food is brought onto a table, or weapons present? I think basically I'm asking just what can the magic mouth 'see' or 'hear' in order to trigger.

Bless you, you've given me a fantastic idea for a dumb trap design called "The Hall of Fire". In the dungeon reference this "hall of fire" at least once and describe it as being a cruel and unrelenting assault on the mind and body.

Long story short it's a hallway at most 60 ft long, and there are at least a dozen of these mouths making harsh HARSH random comments aimed and seemingly the party. Calling out toward the PC's like, the big guy, his mama so fat..., the little one there, I tell you he so skinny..., damn I didn't know the clone spell could fail, look at that thing over there!. Just let the PC's assume what they assume but play it off as a bit of a joke. Point is, enter this hall, prepare to be Roasted.

To add insult to injury, have a large tome set on a pedestal to the right hand side of the exit door with a simple sign that reads (If the burns were too harsh) The book is the actual trap. Glyph of warding releasing a Cone of Cold along the whole hallway.

Condition: A book entitled "The Sacred Texts" being opened.

Words "According to all know laws of aviation...."

Magic Mouth is magic, so it sees and hears everything that can be seen or heard, no perception check required. Yes, you could do the first, but it wouldn't let you actually detect someone, they would still be hidden. "The number of people observing the room" isn't a visible or audible cue, so that wouldn't work. If poison or a weapon is visible, then those triggers would work, but I doubt poison would be, and I doubt it's useful for it to detect visible weapons.

Thanks for the clarification. That was how I was running the spell but it's good to get a second opinion on it.

Quote from Jety_Lefr >>

I've come up with a number of lovely uses for this spell, but my favourite so far is enchanting a statue of a god to speak to its followers!

There's no described limit on how many times the spell can be cast on a single object, so over time you could string together hundreds of these things to all trigger after the previous one finishes speaking. You could macro the statue to say whatever you want if you've got time and enough creativity. Even a one time application of 25 words could do a lot of moral damage or lead to greater physical damage via friendly-fire if the dice roll well.

 Doesn't chaining them require a separate trigger for each message?

I could see a chain effect akin to the holograms of Thor in "SG-1", where the MM "answers" a question, but not one where there's a kind of MM filibuster.

Quote from BadhandsBob >>

enter this hall, prepare to be Roasted.

 Does the MM get Don Rickles' voice? ;p

hey we are all about being inclusive here

Quote from Caladrel >>

Is that an exclusive "or," 

Quote from Giffard >>

I realized that since this spell can be triggered multiple times until it's dispelled you could totally make walls have a conversation with its self any time someone enters a hallway.

"Hey, what're THEY doing here?"

"Don't know but they're UUUUGGGGGLLLLLLYYY,"

and so on.

 

 Cast it on some fancy portraits, and you’re halfway to recreating Hogwarts.