Riddonkulous

I am small enough to hide in your hand Yet I can open places that others cannot understand I have little teeth but never can bite And I spend most of my life away from the light I may live in a pocket or hang by a ring I turn in silence and make locked things sing One little twist can change everything And suddenly freedom is what I bring I have opened doors to houses and rooms And guarded treasures from thieves and tombs Lose me once and your peaceful day Can quickly become a search and pray What am I