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 State of Multiple Devices
  description: |
    ## Link On/Off State of Multiple Devices v1.0.1

    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.

    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)
  domain: automation
  homeassistant:
    min_version: 2022.5.0
  input:
    linked_entities:
      name: Entities to link
      selector:
        entity:
          multiple: true

mode: restart
max_exceeded: silent

variables:
  linked_entities: !input 'linked_entities'

trigger:
- platform: state
  entity_id: !input 'linked_entities'

condition:
- condition: template
  value_template: '{{ trigger.to_state.state != trigger.from_state.state }}'
- 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 }}'

You're my hero :) Thanks