Fullscreen Health Warning

[Viridis]

Does anyone know of an addon that displays a fullscreen warning at a certain health percentage? Or perhaps makes the fade around the edge of the screen at say 60% that gets less transparent as your health goes down?

I know a couple of unitframes do this but it needs to be in a standalone addon, or perhaps I could steal the code from something?

I've started using RothUI and sometimes I miss my low health. Thanks for reading.