If you have an Android device, you could do this with SharpTools for Android.
Alternatively, I’ve seen people setup Twilio accounts and run a script to react to SMS changes.
Here’s some details on the Android based approach:
Edit: In the above image “Friend’s Phone” would be the SMS coming from your alarm system.
Tasker would be setup such that whenever an SMS is received, it would tell SharpTools to control the garage door on SmartThings.
- In Tasker, create a new Profile → Event → Phone: Received Text
- Configure the profile with your desired filters (who it came from, what the message says)
- Configure the action to take your desired SmartThings action via SharpTools
