Since version 23.01.14 NetAlertX uses a simple timestamp-based version check to verify if a new version is available. You can check the current and past releases here, or have a look at what I'm currently working on.

If you are not on the latest version, the app will notify you, that a new released version is avialable the following way:

If any notification occurs and an email is sent, the email will contain a note that a new version is available. See the sample email below:

In the UI via a notification Icon and via a custom message in the Maintenance section.

For a comparison, this is how the UI looks like if you are on the latest stable image:

During build a /app/front/buildtimestamp.txt file is created. The app then periodically checks if a new release is available with a newer timestamp in GitHub's rest-based JSON endpoint (check the def isNewVersion(): method for details).