The answer? Nope, it's a fob (fauxb?). Much like the voices that Homeland's Carrie sometimes hears in her head, it's an illusion, courtesy of hairstylist Peter Butler.
The style is a feat of engineering, involving some clever styling techniques and a savvy use of products (four different John Frieda products, in this case). Butler prepped Danes's hair with Frizz-Ease Thermal Protection Formula Hair Serum and Frizz-Ease Curl Reviver Styling Mousse, which added texture to make the hair more workable. Then comes the magical part.
Butler gave Danes a low side part and used a large-barreled curling iron to curl her hair inward. (Hair DIY'ers please note: The curling iron also added some of that unbelievable smoothness to the style.) He then created two small pin curls at the nape of her neck, which is a trick I've seen backstage a lot--it gets rid of bulk. Butler then combed the top of her hair down and under, pinning into the base. He finished off with hairspray, and what I think is the key product, Frizz-Ease 100% Shine Glossing Mist. Her hair looked incredibly shiny and healthy last night.
Chop your hair for real, Claire!