Hi Amper
What fun this thread is. We used to have four chickens and good layers they were. They were very much creatures of habit and would start getting anxious when the sun started going down and go into their coop for the night. And at sun-up they would be fussing to be free in the garden, especially as we spoilt them to hell with little treats. They were battery hens rather than mains and when their feathers grew, I taught two of them to fly a bit.
I too have thought about a solution to Mr *&%#! fox and the best low-tech approach that I came up with, is to have a medium size, but aggressive dog living with the chickens to look after them. You would not need to worry about locking doors or anything else then.
An alternative approach is to have the chickens unlock the door themselves- don't laugh...yet
So how does the chicken operated lock work:
Chickens are not the brightest of birds, but they are not totally dumb either, especially when food is concerned. So what I table is two pads, one just outside the door and one just inside the door, which the chickens have to peck a number of times before the door opens. Of course, a new chicken would not know what to do, but it would not take long for them to learn, especially if their food is in the coop. I was going to try this approach out, but our chickens left for a posher neighborhood before I got around to it. But I did try out a few similar tasks for them to carry out before they got a treat, and they managed without any problem. They weren't very good with simultaneous equations though.
The actual keypad could be made so that only a chickens beak could operate it, so that any smart-arse fox, even if he knew the code, would not be able to operate the lock with his paw or nose, but I think it is unlikely that a fox would figure out how to operate the lock anyway.
I will get my coat now.