The Carolina Chickadee’s most famous call is the familiar chick-a-dee-dee-dee from which comes its name. We have heard it said that the number of dee’s is a form of an alarm call with more dee’s indicating a higher level of threat.
These tiny, beautiful little black and white birds hop along tree branches searching for insects, sometimes hanging upside down or hovering.
Carolina chickadees are so similar to Black-capped Chickadees that they themselves have trouble telling their species apart.  Here in Atlanta you can pretty well bet that it’s a Carolina Chickadee that you’ve seen because the southern-most range of the Black-capped is extreme north Georgia
Insects form a large part of their diet, especially in summer; seeds and berries become important in winter. They sometimes hammer seeds on a tree or shrub to open them; they also will store seeds for later use. 
Carolina chickadees are able to lower their body temperatures to induce an intentional state of hypothermia called torpor. They do this to conserve energy during cold winters. In extremely cold weather conditions, they look for cavities where they can hide in and spend up to fifteen hours at a time in torpor. 
References and Additional Information
 Wikipedia: Carolina Chickadee
 The Sibley Guide to Birds, second edition – David Allen Sibley
 Cornell – All About Birds: Carolina Chickadee
 Cornell – All About Birds: Carolina Chickadee – sound
 The Breeding Bird Atlas of Georgia – UGA Press: Schneider, Beaton, Keyes and Klaus, Eds.