Lockitron[1] is not what he built, but is just the latest product to have been curated.

Lockitron is a YC-company and, to answer your question, this is from the Lockitron FAQ:

Unlike lost keys which anyone can use to unlock your door, in the event you lose your phone you can disable its access by resetting your account password. Never worry about changing your locks again.

[1] - http://lockitron.com/