Wi-Fi or a mobile data connection are only required for initial app setup (downloading / installing the app, creating an account, or signing in) and sharing your glucose information with your care team or with other connected apps. The app does not require a Wi-Fi or a mobile data connection to scan your sensor or to record your current glucose readings. ¹ During periods when your phone is operating in a disconnected state, your data will only be uploaded to LibreView after a Wi-Fi or mobile data connection is restored.

Reference:

1.  FreeStyle Libre flash glucose monitoring system User's manual.