Select multiple entities to link their on/off 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 State of Multiple Devices
  description: |
    ## Link On/Off/Brightness/Color Temp of Multiple Devices v1.1.2

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

    You can select any entity, but only entities supported by the `homeassistant.turn_on` or `homeassistant.turn_off` service calls will work.

    ### Requirements
    * All selected entities MUST suport `homeassistant.turn_on` and `homeassistant.turn_off` or errors will be logged and the blueprint will not work.
    * Requires Home Assistant 2022.5.0 or newer.
    
    ### Credits
    * [@adchevrier](https://community.home-assistant.io/u/adchevrier) for the [initial blueprint](https://community.home-assistant.io/t/synchronize-the-on-off-state-of-2-entities/259010)
    * [@hebus](https://community.home-assistant.io/u/hebus) for [this fantastic template](https://community.home-assistant.io/t/synchronize-the-on-off-state-of-2-entities/259010/38)
    * [@dbrand666](https://github.com/dbrand666) for [various fixes](https://gist.github.com/dbrand666/b731672b2a282b9afd51a97e6e5c2b2b)
    * [@jmaroeder](http://github.com/jmaroeder) for [adding brightness](https://gist.github.com/jmaroeder/c0952533a3f2c746eef83db268ddbbba)
  domain: automation
  homeassistant:
    min_version: 2022.5.0
  input:
    linked_entities:
      name: Entities to link
      selector:
        entity:
          multiple: true
    transition:
      name: Transition
      selector:
        number:
          min: 0
          max: 3600
          unit_of_measurement: seconds
      default: 0
mode: restart
max_exceeded: silent
variables:
  linked_entities: !input linked_entities
  transition: !input transition
trigger:
- platform: state
  entity_id: !input linked_entities
- platform: state
  entity_id: !input linked_entities
  attribute: brightness
condition:
- condition: template
  value_template:  >
    {{ trigger.to_state.state != trigger.from_state.state or 
       (trigger.to_state.attributes.brightness is defined and 
        trigger.to_state.attributes.brightness != trigger.from_state.attributes.brightness) or
       (trigger.to_state.attributes.color_temp is defined and
        trigger.to_state.attributes.color_temp != trigger.from_state.attributes.color_temp) }}
- condition: template
  value_template: '{{ (trigger.to_state.state == "on") or (trigger.to_state.state == "off") }}'
- condition: template
  value_template: '{{ trigger.to_state.context.parent_id is none or (trigger.to_state.context.id != this.context.id and trigger.to_state.context.parent_id != this.context.id) }}'
action:
- service: homeassistant.turn_{{ trigger.to_state.state }}
  target:
    entity_id: '{{ expand(linked_entities) | selectattr("entity_id", "!=", trigger.entity_id) | map(attribute="entity_id") | list }}'
  data: >
    {% if trigger.to_state.state == "on" %}
      {
        {% if trigger.to_state.attributes.brightness is defined -%}
        "brightness": {{ trigger.to_state.attributes.brightness }},
        {%- endif %}
        {% if trigger.to_state.attributes.color_temp is defined -%}
        "color_temp": {{ trigger.to_state.attributes.color_temp }},
        {%- endif %}
        "transition": {{ transition }}
      }
    {% else %}
      {}
    {% endif %}