Open sesame!

A British chicken-lover has thought up a unique door opener which the birds themselves can use. The last chicken to go to roost closes the door behind it. In the morning the door opens when all the chickens leave their roost.
Andrew Wells wanted a system for which neither a caretaker nor electricity was needed, but that ensured that the chicken coop door was closed at night to keep foxes out. He wanted the door to stay open until all the chickens were inside, and he wanted it to open automatically in the morning. Wells was able to construct his desired system with a smart design using a counterweight on the roost where the chickens sleep. It took a bit of tinkering to find the correct weight, but then it worked just fine. Of course the weight must be adjusted when more or fewer chickens go to roost, as when one of them is broody. This system, easily viewed in the accompanying YouTube video, works for as many as 12 chickens.
Look at the YouTube video