There are some pretty cool smart doorbells out there, but they are expensive and the basic components of a wireless button, camera and a small computer are cheap! In fact the most expensive component in this project is the camera module, which is still a bargain at sub 20 USD.
An overview of the system is shown in Figure 1. When someone pushes the doorbell button, the button module transmits a 433 MHz RF signal to a receiver (not show) which sounds a chime. However, the RF signal can be freely intercepted (not ideal for security but pretty convenient), and here an RF module attached to a Raspberry Pi is used to intercept the RF signal. On receiving the signal, the Pi takes an image using the camera. This image can then be sent as a mobile notification, for example using the Telegram app. In this project, I actually send the image to my home automation system, Home-assistant.
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