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 On/Off/Brightness State of Multiple Devices
  description: |
    ## Link On/Off/Brightness State of Multiple Devices v1.1.1

    Select multiple entities to link their on/off and brightness state. If any selected entity is turned on or off, or its brightness 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)
  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 != trigger.from_state.attributes.brightness }}'
- 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" %}
      {"brightness": "{{ trigger.to_state.attributes.brightness }}", "transition": "{{ transition }}"}
    {% else %}
      {}
    {% endif %}

doesn't work for devices that dont have a brightness

Suggested change to support 2024.10 syntax. Note that line:

Modified for 2014.10 syntax (triggers: trigger, etc) AND min_version - SoundOfMind, 2024 10 02

can be removed. I don't deserve any credit - you and the other contributors did the hard work.
Thanks!

blueprint:
name: Link On/Off/Brightness State of Multiple Devices
description: |
## Link On/Off/Brightness State of Multiple Devices v1.1.1
## jmaroede/link_multiple_devices.yaml
## Modified for 2014.10 syntax (triggers: trigger, etc) AND min_version - SoundOfMind, 2024 10 02

Select multiple entities to link their on/off and brightness state. If any selected entity is turned on or off, or its brightness 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)

domain: automation
homeassistant:
min_version: 2024.10.0
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
triggers:

• trigger: state
  entity_id: !input linked_entities
• trigger: state
  entity_id: !input linked_entities
  attribute: brightness
  conditions:
• condition: template
  value_template: "{{ trigger.to_state.state != trigger.from_state.state or trigger.to_state.attributes.brightness != trigger.from_state.attributes.brightness }}"
• 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) }}"
  actions:
• action: 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" %}
  {"brightness": "{{ trigger.to_state.attributes.brightness }}", "transition": "{{ transition }}"}
  {% else %}
  {}
  {% endif %}