This How-To is all about custom notifications triggered from Salesforce and sent to your phone.
This project involves building a Flow that leverages the Decision, Assignment, and Action elements. The result: Custom notifications on your phone that trigger when an opportunity is within 7 days of closing!
You can apply this knowledge to create your own notifications on a standard or custom object and trigger on whatever you fancy.
Here is the code snippet referenced in the how-to:
SELECT ID, CustomNotifTypeName FROM CustomNotificationType