If my month-long foray into electronics had no other benefit, at least now I have an AC detecting pen so I don't die while fucking around with light switches, and I can find which of the batteries scattered in the bottom of my wardrobe are dead.

@Demolishun They're especially nice because they're super easy and quick to use so there's no temptation to measure first and then try to remember or extrapolate the state of various conductors, I can just measure over and over again when I get uncertain or find a new metal surface that isn't visibly connected to one I'm sure about.