Let's get straight to the point. I have an iPhone 5S, and yesterday I was walking to class with a cold water bottle in my right hand and my books in my left hand, iPhone in my hoodie pocket. When I got to class and set everything down, I reached for my iPhone and placed my thumb on the home button to unlock it... "Try Again". I tried again and again and it never unlocked. It was then I noticed that my fingertips were cold from holding the water bottle during the 3 min walk to my class. Later after class - when my fingertips had warmed up, the phone unlocked after the first try. Later that night, I tried unlocking the iPhone with my left thumb - try again. Turns out, Touch ID doesn't like dry/cracked skin. Anyone else experiencing this?! This winter is going to be fun!