Building a Smart Doorbell with Zigbee, MQTT, and Raspberry Pi

This is a smart doorbell project that came together right after I set up a Zigbee + MQTT hub.

One of my first goals after setting up my homelab was to set up a hub for smart home automation. With Nomad, setting up all the prerequisites was straightforward:

• Mosquitto — an MQTT broker
• zigbee2mqtt — a bridge between Zigbee and MQTT
• Home Assistant — a dashboard and control center for smart home devices

Zigbee2MQTT was a fantastic surprise: it’s practically plug-and-play and extremely powerful. I’m using an open hardware Zigbee dongle and a few well-known compatible devices, so I expected it to work, but I was blown away by how seamless it was. I made sure the z2m instance had access to the right /dev/ on the host, turned on pairing mode, and it instantly started sending data to my MQTT instance.

Nomad HCL for Zigbee2MQTT:

job "zigbee2mqtt" {
  type = "service"

  group "zigbee2mqtt" {
    count = 1

    service {
      name = "zigbee2mqtt-web"
      port = "http"

      tags = [
        "traefik.enable=true",
        "traefik.http.routers.z2m.rule=Host(`z2m.home.arpa`)",
      ]
    }

    network {
      port "http" {
        to = 8080
      }
    }

    task "server" {
      driver = "docker"

      env {
        TZ = "Europe/London"
      }

      config {
        image = "koenkk/zigbee2mqtt"

        privileged = "true"

        ports = [
          "http",
        ]

        volumes = [
            "/srv/section9/zigbee2mqtt/data:/app/data",
        ]

        // Access zigbee dongle
        devices = [
          {
            host_path = "/dev/serial/by-id/usb-1a86_USB_Serial-if00-port0"
            container_path = "/dev/ttyACM0"
          },
        ]
      }
    }
  }
}

The doorbell project

I’d already picked up a few affordable Zigbee sensors and controls, hoping to find some interesting uses for them.

Then, inspiration struck: my doorbell is broken. Eventually I want to fix it, it’s nice looking retro bakerlite thing, but the contacts are burnt out. My initial plan was to replace it temporarily with a wireless model, but why not make a smart doorbell instead?

I had already paired a Zigbee switch and verified it was sending data smoothly to MQTT. And since I had a Raspberry Pi set up as a hi-fi speaker (my “Pi-Fi”), it was all ready to go — typically used with AirPlay, but essentially a Linux box with a [hi-fi amp hat].

I just needed to play a sound in response to an MQTT event. So, I downloaded a doorbell sound, tested it with aplay, and ran a mosquitto_sub to confirm the topic I needed to subscribe to. Sound, check. Events, check.

The speaker and zigbee button.

…And then the dreaded bikeshedding brain kicked in: “Should I write a program for this? What language? JS/Node is familiar, but maybe I should try something new? Which MQTT library? Should I launch aplay from the app, or find an audio library?” Thankfully I snapped out of it — why not keep it simple and use the command-line tools I’d just tested? KISS.

After a quick search, I found an example and adapted it to my needs:

#!/usr/bin/env sh

echo "Starting doorbell..."

# `home.arpa` is the mqtt broker
# `zigbee2mqtt/cmd/controls/doorbell/action` is the topic published by z2m when the button is pressed
mosquitto_sub -h home.arpa -t zigbee2mqtt/cmd/controls/doorbell/action |
    while read payload ; do
       echo "Doorbell rang!"
       aplay /opt/doorbell/doorbell.wav
    done

echo "Doorbell stopped."

I set up the necessary systemd configuration to run this as a service on the Pi-Fi.

I was tempted to post a video, but filming a speaker playing a sound isn’t that compelling 😂

And the final cherry on top: Home Assistant can also subscribe to MQTT and includes an automation feature. Now, when the doorbell is pressed, I get a notification — even on my watch!

Home assistant notification on my watch.

This was so satisfying to implement — simple in approach, but fully leaning into the sophisticated software stack I already have running.