I purchased one of those wireless temperature monitors. I think I paid about 10$ at WalMart. My husband placed the sender on a rafter in the coop, I've been keeping the monitor in my kitchen to read the temp inside the coop. This morning it read 28 degrees F, and then dipped down to 22, which was I think when the door was opened. Right before I left for work I quickly checked everyone's toes and combs for frostbite- which I assume would make the skin look black? So far, no frostbite I can tell of.