Getting from simple notifications on state change, to remote phone SMS notification

Going away tomorrow for a week. I have a camera and separate motion detector that are working properly to trigger events such as lights.
I tried my first persistent notify today just to see if I could get a notification. Code below, it worked fine. How do I get from here to having a notification send me something to my phone, like an SMS?

I couldn’t find a blueprint that did what I wanted. Do I need a GSM modem? Is this even possible without using an online paid service?

alias: Notify
description: ""
  - platform: state
      - binary_sensor.birch_neolink_1_motion
    to: "on"
      hours: 0
      minutes: 0
      seconds: 1
condition: []
  - service: persistent_notification.create
      message: Trigger is working
mode: single

This should work (instead of SMS):

You mean just using the mobile app (called Home Assistant it seems, not Companion) and looking for the notification?
I want to be alerted in some way.

Yes, the mobile app (companion app) supports receiving notifications. Install the Home Assistant app on your phone, follow the instructions in the link above for notifications, and you can receive home assistant notifications on your phone.

I use this to get important notifications when certain events happen (using automations to send the notifications).