People won’t know where the message comes from, they’ll just hear your voice as though you were standing next to them. Everyone hears it at the same time. The message is not translated into anyone’s native language, everyone hears it exactly as you say it. The maximum length is 6 of your breaths.
“Psychopaths no longer exist. Only people with fully-developed frontal lobes exist.”
Immediately followed by everyone from the former category drops dead, and no new ones will ever be born.