Main power Indicator

[Firehousepinball <mixinguiness@xxxxxxxxx>]

Hey all, I would like to make a simple circuit that will power an LED
when I am being fed from the grid. This way I can tell at a glance
when I am running on backup power when the Grid returns. I have no
problem tapping into the main at the panel, and would possibly like to
add a relay to this as well to trigger an audible alert.

Are there any specifics that I should watch out for? I want this to be
safe.

Thanks