For one, it only takes a small radio receiver to detect lightning strikes, and [mircemk] shows us exactly how to do that. When lightning flashes, it also lights up an incredibly wide spectrum of ...

TK has combined a PIR with an Arduino to create a smart safety light for the house or workshop. Follow along as this gets built out into a more extensive project.

You can make a perfectly good water detector with things you probably already have around the house. My point isn’t that you should (or shouldn’t) construct a homemade water sensor.