Within a decade, you won't have to carry keys.
This app let's you unlock your door using your phone and you can store the unlock code encrypted in the cloud.
You can also open it remotely or pass a key to your friends to use temporarily.
In addition, using near-field communication, you can wave your phone in front of the lock to open it.
While the video below shows Lockitron in action, you can read more about it here.