Had been fascinated by this concept for a while now. Logging in to all my favorite websites with a single master key. A real key in my key chain.
Key is a little device that helps you login to your web services and apps on any device based on your fingerprint and simple turn gestures. That way you can use a borrowed device as comfortably as your personal device without having to worry about signing the previous users out and entering your passwords individually for all the services.
As a metaphor for the real world key that opens the door to our personal spaces, the key here lets us in to the digital world. Ironically, this key acts as a digital locker.