Send notification if and when a network device loses connectivity

device_connectivity_notification.yaml

blueprint:
  name: Device Connectivity Notification
  description: Send a notification if a networked device loses connectivity
  domain: automation
  input:
    server_group:
      name: Server Group
      description: This group of servers will be monitored for potential loss of connectivity
      selector:
        entity:
          domain: group
    notify_device:
      name: Device to notify
      description: Device needs to run the official Home Assistant app to receive notifications
      selector:
        device:
          integration: mobile_app
    message:
      name: Message
      description: Notification message to send to Home Assistant app
      default: " Network connection lost for devices: {{ disconnected_servers }} "

trigger:
  - platform: state
    entity_id: !input server_group
    from: "on"
    to: "off"

variables:
   disconnected_servers: "{{ expand('group.servers')
                           | selectattr('attributes.device_class', 'eq', 'connectivity')
                           | selectattr('state', 'eq', 'off')
                           | map(attribute='name')
                           | list }}"

action:
  domain: mobile_app
  type: notify
  device_id: !input "notify_device"
  message: !input "message"