We've seen a few smart door projects here at The MagPi, but nothing quite as cool as this SMS doorbell that links up to your mobile phone.
This doorbell snaps a photo of a person when they call, sends you a SMS/text message with their photo, and then lets you phone your doorbell to talk to them.
It's always interesting to see people hooking up their homes to Raspberry Pi boards, and this is one of most integrated smart home projects we've seen.
How to build a RaspberryPi Door Spi
The system works using a Raspberry Pi and a GSM-BoB module. Specifically this M95 by Quectel.
You can even send an SMS from your phone, containing a passcode that opens the door (via a relay).
More information on the build can be found at Elektor Magazine.