Blog: For just $2, convert any existing wired doorbell into a smart doorbell; using ESPHome and Home Assistant: https://frenck.dev/diy-smart-doorbell-for-just-2-dollar/

doorbell.yaml

---
esphome:
  name: doorbell
  platform: ESP8266
  board: esp01_1m

# WiFi connection, correct these
# with values for your WiFi.
wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password

# Enable logging.
logger:

# Enable Home Assistant API.
api:

# Enable over-the-air updates.
ota:

# Enable Web server.
web_server:
  port: 80

# Sync time with Home Assistant.
time:
  - platform: homeassistant
    id: homeassistant_time

# Text sensors with general information.
text_sensor:
  # Expose ESPHome version as sensor.
  - platform: version
    name: Doorbell ESPHome Version
  # Expose WiFi information as sensors.
  - platform: wifi_info
    ip_address:
      name: Doorbell IP
    ssid:
      name: Doorbell SSID
    bssid:
      name: Doorbell BSSID

# Sensors with general information.
sensor:
  # Uptime sensor.
  - platform: uptime
    name: Doorbell Uptime

  # WiFi Signal sensor.
  - platform: wifi_signal
    name: Doorbell WiFi Signal
    update_interval: 60s

# Global to store the on/off state of the chime
globals:
  - id: chime
    type: bool
    restore_value: true
    initial_value: 'true'

# Exposed switches.
switch:
  # Switch to restart the doorbell.
  - platform: restart
    name: Doorbell Restart

  # Switch to turn on/off the chime.
  - platform: gpio
    id: relay
    inverted: true
    name: Doorbell Chime
    pin: GPIO0

  # Switch to turn on/off chime when
  # doorbell button is pushed.
  #
  # It creates a "virtual" switch based
  # on a global variable.
  - platform: template
    name: Doorbell Chime Active
    id: chime_active
    restore_state: false
    turn_on_action:
      - globals.set:
          id: chime
          value: 'true'
    turn_off_action:
      - globals.set:
          id: chime
          value: 'false'
    lambda: |-
      return id(chime);

# Binary sensor representing the
# Doorbell button push.
binary_sensor:
  - platform: gpio
    id: button
    name: Doorbell Button
    pin:
      # Connected to GPIO on the ESP-01S.
      number: GPIO2
      mode: INPUT_PULLUP
      inverted: true
    filters:
      # Small filter, to debounce the button press.
      - delayed_on: 25ms
      - delayed_off: 25ms
    on_press:
      # Only turn on the chime when it is active.
      then:
        if:
          condition:
            - switch.is_on: chime_active
          then:
            - switch.turn_on: relay
    on_release:
      # On release, turn of the chime.
      - switch.turn_off: relay

home-assistant-doorbell-camera.yaml

---
# This automation triggers when the doorbell button is pushed
# and out the front door camera stream to the tv.
#
automation:
  - alias: "Doorbell Camera"
    trigger:
      platform: state
      entity_id: binary_sensor.doorbell_button
      to: 'on'
    action:
      - service: camera.play_stream
        data:
          entity_id: camera.front_door
          media_player: media_player.living_room_tv

home-assistant-doorbell-chime.yaml

---
# Turns off the doorbell chime after 8pm.
# Turns it on again in the morning @ 7am.
#
automation:
  - alias: "Doorbell off after 8pm"
    trigger:
      platform: time
      at: "20:00:00"
    action:
      service: switch.turn_off
      entity_id: switch.doorbell_chime_active

  - alias: "Doorbell on after 7am"
    trigger:
      platform: time
      at: "07:00:00"
    action:
      service: switch.turn_on
      entity_id: switch.doorbell_chime_active

home-assistant-doorbell-notification.yaml

---
# This automation triggers when the doorbell button is pushed
# and sends out a notification to our Apple iPhones/watches.
#
automation:
  - alias: "Doorbell Notifications"
    trigger:
      platform: state
      entity_id: binary_sensor.doorbell_button
      to: 'on'
    action:
      - service: notify.mobile_app_frencks_iphone
        data:
          title: Doorbell
          message: Ding dong! Someone is at the door!
          data:
            attachment:
              content-type: jpeg
              url: http://tiptag.com.ar/wp-content/uploads/2018/06/timbre1.jpg
      - service: notify.mobile_app_ninja_iphone
        data:
          title: Doorbell
          message: Ding dong! Someone is at the door!
          data:
            attachment:
              content-type: jpeg
              url: http://tiptag.com.ar/wp-content/uploads/2018/06/timbre1.jpg