It's my understanding that the pump power source should be directly (fused) from the ships batts so if unattended at the berth it will function with the main D/C switch off or if the main D/C panel goes "poof".
bell and light are good but I also remember an idea, and have utilized it, to route
the pump discharge into the cockpit
- if I don't hear the alarm
bell or see the light, I'll get the "hint" with wet feet! It also simply drains thru the cockpit
drains rather than have another hole thru the boat (even if it is above the waterline).
My 2-cents :-)