Wireless Internet WiFi Doorbell Project Kit for Raspberry Pi.
The wireless receiver board attaches to your Pi, your Pi is connected to the internet. When someone pushes the doorbell, the Pi detects this and sends an email to your mobile phone. If you have the Raspberry Pi camera module, you'll get a HD photo emailed to your phone too.
You can expand the system with inexpensive Lloytron MIP wireless PIRs & magnetic door sensors, or even a 2nd doorbell. All the Lloytron MIP devices have a unique code, a bit like the MAC address in your WiFi & Bluetooth devices, and can be individually identified by our receiver code running on the Pi.
(Doesn't include a Raspberry Pi, Raspberry Pi camera or Raspberry Pi case)
For Raspberry Pi A, B, A+, B+, Pi 2 and Pi 3 models.
(Also Pi Zero if you have soldered a GPIO header on)