Weather Hens
If you study the above photo carefully you can see that the hens are both out of their home. That means it's going to rain. If one is out and the other is in, it means sleet is on its way. Two in means its raining or snowing or, if the door of their house is nailed shut there's a big blow on the way in. If neither hens are to be seen, they have either been blown away or else they are in the pot!
A full-proof system