Select multiple entities to link their on/off and brightness state. If any selected entity is turned on or off, the other selected entities will be sent a matching on or off command.

link_multiple_devices.yaml

blueprint:
  name: Link On/Off/Brightness State of Multiple Devices
  description: >

    ## Synchronize Entities for On, Off, and Brightness Control

    This blueprint allows you to synchronize multiple entities for controlling their on/off state and brightness level. It simplifies the experience of managing devices by ensuring they respond consistently, regardless of which entity you use.

    ### Overview

    Imagine you have two wall switches in your corridor. Turning on the first one will also indicate the light's status on the second switch. You can adjust brightness from any device, whether it's a mobile app or a physical switch.

    ### Key Features

     - When one entity is turned on or off, the others will follow suit.
     - Changing brightness on one entity will update the brightness for all linked entities.

    ### Requirements

     - Brightness attribute must be a numeric brightness value, not a step up/down indicator.
     - All selected entities MUST support `homeassistant.turn_on` and `homeassistant.turn_off`.
     - Tested on Home Assistant version 2023.09.

    ### Tested Devices

     - Moes wall smart switch (non-dimmer)
     - Moes wall smart switch with dimmer functionality
     - Shelly Dimmer 2

    ### Credits

    - Inspiration and starting point from @aderusha's [Link On/Off State of Multiple Devices](https://gist.github.com/aderusha/4d2c8600a2e4771b91b8efc555946413)

  domain: automation
  author: Bengt Thuree 
  source_url: https://gist.github.com/bthuree/a494ad7dfd5133d3a2bf4b29f9ed68e9

  input:
    linked_entities:
      name: Entities to link
      description: Entity to be syncronized/linked
      selector:
        entity:
          multiple: true

mode: single
max_exceeded: silent

variables:
  linked_entities: !input linked_entities
  initiating_automation_id: null  

trigger:
- platform: state
  entity_id: !input linked_entities
  id: linked_entities_trigger  

condition:
  condition: and
  conditions:
  - alias: Verify valid to states (on, off)
    condition: template 
    value_template: "{{ trigger.to_state.state in ['on', 'off'] }}"  
  - condition: or
    conditions:
      - alias: Either on/off has changed
        condition: template
        value_template: "{{ trigger.to_state.state                     != trigger.from_state.state }}"
      - alias: or brightness has changed
        condition: template
        value_template: "{{ trigger.to_state.attributes.brightness|int != trigger.from_state.attributes.brightness|int }}"

action:
- if:
    - alias: If action is to turn on the lights
      condition: template
      value_template: '{{ (trigger.to_state.state == "on") }}'
  then:
    - if:
        - alias: then, also check if brightness is present
          condition: template
          value_template: "{{ trigger.to_state.attributes.brightness is defined }}"
      then:
        - alias: if so, turn on lights and set brightness
          service: homeassistant.turn_on
          target:
            entity_id: "{{ linked_entities | reject('eq', trigger.entity_id) | list }}"
          data:
            brightness: "{{ trigger.to_state.attributes.brightness }}" 
      else:
        - alias: otherwise turn on lights (skip brightness)
          service: homeassistant.turn_on
          target:
            entity_id: "{{ linked_entities | reject('eq', trigger.entity_id) | list }}"
  else:
    - alias: else turn of lights only
      service: homeassistant.turn_off
      target:
        entity_id: "{{ linked_entities | reject('eq', trigger.entity_id) | list }}"