We don't have windows on the interior of the house that look out to the street. The "front" door actually opens up to the atrium, so currently, when someone is at the front door, we have no idea who it is, except for a blurby shadow behind a glass wall. (Kinda creepy). I'd love to pick up one of these newfangled gadgets: the Doorbot and Lockatron, recently funded on Christie Street. Doorbell and security camera (accessible via mobile phone to boot!)
Added feature is the lockatron functionality, so you can virtually unlock the door.
photos: Christie Street