Angus, I think you were the only one to catch the Flux Gate Capacitor reference.
This is what Jabsco actually says about it.
"The Rule Mate series of Bilge pumps feature a solid state water
sensing technology that eliminates the need for a separate
When water enters the bilge and reaches a certain height (2-3/4 inches) a
sensor turns the pump on. After the water is pumped out, another sensor
shuts the pump off.
The sensor’s unique “field effect” technology will only recognize water. If
a 100% concentration of oil is detected the pump will not activate. This is
not a zero discharge prevention system."
I have no idea what field effect technology is, there for it must be a Flux Gate Capacitor.
Whale and Johnson also make pumps that use field effect to turn them on and off.
The Water Witch switch does not use field effect. It uses two contacts and the conductivity of water to turn the pump on.