Actually, the problem with my alarm wasn't corrosion due to excess current draw, but corrosion due to my probes being copper and suspended over a constantly wet sump pit. The petina that developed was so bad, it failed to alert when needed. I plucked it up off the edge, put my wet finger across the two screws on the top (nickel plated, I think), and off it went. I then flipped it over, and there was my problem. The wires, solder, connections, and components were all good - just the copper went bad. Hence, my recommendation for galvanized probes.
Remember, I also built this to use as a continuity tester, which I threw into a small cardboard box. That was... gee!... 14 years ago, and it's still working. So, input impedance had nothing to do with it. One had copper terminals, the other just regular alligator clips. It was enviornment and materials, not current draw when activated (practically NO current draw when idle - no on/off switch is needed!).
nop