Recently connected my bilge pump alarm to 12v relay, so when the bilge pump (float switch) turns on, the external sensor on my webcam triggers.
Now I get an email whenever the bilge pump turns on. I get an email like this one:
Some short wires and crimped connectors <$10
12v relay from Radio Shack <$10
Total cost: less than $20
(I already have the webcam sending me pictures when it detects motion on the boat. They go for about $50. And it takes about 1.5 amps to drive it and the long range WiFi setup.)
I have a separate, different relay to use when I care more about staying connected to shore power, like in a slip in winter time.