You implant a message within an object, a message that is uttered when a trigger condition is met (determined by you). Choose an object that you can see and that isn't being carried by another creature. Then speak the message, which must be 25 words or less, though it can be delivered over as long as 10 min.
When that circumstance occurs, a magical mouth appears on the object and recites the message in your voice and at the same volume you spoke. When you cast this spell, you can have the spell end after it delivers its message, or it can remain and repeat its message whenever the trigger occurs. See PHB for expanded details.
a small bit of honeycomb and jade dust worth at least 10gp, which the spell consumes