i remember about an addon, but i can't find it anymore, btw, this addon
just use Say/Yell/Party/Raid or desired chat channell, with a custom text, it was turned on when the player reach a desired value of mana, health, or if an enemy where spoted, this last case was turned on by an hot-key
it was called Sentinel Tower, or something like this... i realy can't remember the exact name, but i'ts a pair of days that i'm searching for something like this