They are called Diadophis punctatus. Most of the ringneck snakes are not poisonous and you can keep them at home. See here for reference:

 If you are talking about the ones in New England that live near water, then yes they are poisonous. They won't kill you or anything, just might make you sick (throw up, diarrhea, a lot of pain at bite site). Keep at your own risk. I also believe that they only eat fish too, you can buy cheap comet fish for like .50 cents at most pet stores. Hope this helps!

 Are you asking about a ring neck snake that is shiny black with yellow ring and white belly?