Mob at 25% health, warning message

[cawfee]

Heya,

this is primarily for my Affliction warlock who starts Drain Soul if a boss is at 25% of its total health, and have been tinkering around with the "UnitHealthMax("target") / 4" for a bit before realizing that there might already be one out there.

So I was wondering if anyone out there knows of an existing addon that already fills this function before I go ahead and finish mine. All it really does is flash a message for the player once the target unit reaches 25% of its total health, with a slash command to toggle it on and off.

Thanks in advance for your assistance