When a visitor presses the doorbell, DoorPi tells the security camera to take a photo of the visitor which is then sent to the user via SMS. This allows the user to see who is at the door from any location. The photo is also recorded in the app's history. Finally, the app connects to a bluetooth speaker which lights up and plays sound notifying users (including the hearing impaired).
The app was run on the RaspberryPi at the hacathon but you can see a demo version here.