It's quite surprising that anyone in North America would keep a garter snake as a pet, since they are an indigenous species found in the wild here. They belong wild and free, not cooped up in a house. This is just inhumane. I'm sorry for your loss, but that it died of hypothermia because your cell phone was more important than keeping the snake warm, and that you can't even recognize when the animal is dead pretty well underscores that you really oughtn't to have any more snakes as pets. Please leave garter snakes alone.