Patch uses Outlook to send an email to yourself, which triggers a Shortcuts automation to intercept the notification and send the text message.
The whole process takes around ten seconds and requires no interaction after you hit send on the Pebble.
Patch stores Outlook OAuth tokens and contact phone numbers in your Pebble App's browser storage.
If someone can access your device logs, browser/session storage, or your Outlook account, they may be able to view message metadata or send mail. For best safety, create a new Outlook account for Patch.