I have it go off every time the pump runs. I also have a second float switch about a foot up from the main bilge pump switch (deep sump) with a different sounding alarm and a separate alarm light. That one has never gone off except when testing.

Since the shower drain goes to the bilge it always has some water in it - it is a comforting sound when the pump alarm goes off while in the shower.

I also get a lot of rain down through the mast into the bilge. Pretty amazing how much comes in through a few small holes where the running rigging exits the mast.