Sometimes I buy things at the one-dollar shop, just to see what's inside. And then I use some time to think about what I can use it for; other than it's original purpose which I seldom am interested in. That's how I used a pedometer (step counter) to count how many times, if any, someone had used my door-bell while I was away, and a table lamp as my power supply etc. at my table, so I don't have to go to my lab supply. All sorts of strange things fills my appartement. Sometimes I have to open things up, just to remember what on earth I have made and forgotten about.
So what do you buy to have a rain-alarm? A cheap alarm clock of course. What else do you think? :-)
After opening it to see what was there, I found that it was very sensible to moist at the two points marked by arrows. Well, was it sensitive enough for a rain alarm??
I soldered two wires to these points, made a sensor out of a stripboard and tried it out. Meanwhile I had ripped off the hands of the clock, because I do not need another clock. I have the clocks own button for alarm in on-position and try out the sensor.
It works fine. I added a on/off switch to the wires from the clock to the sensor and put the sensor outside my window.