With the update release of the Garmin Varia mobile app 1.5.0 it appears there was a new feature rolled out and defaulted ON.
The release notes list only "Bug fixes."
PLEASE PROVIDE BETTER RELEASE NOTES.
I can't stress this enough especially when it relates to a device such as the Varia Radar. Having new undocumented functionality installed and enabled BY DEFAULT is not good practice. The "All Clear" tone is also extremely different to the detection tone, meaning a lot of people simply have no idea what the sound is and what app/service is causing it.
Having said this - I welcome this update, it's something that should have been there upon release of the 515/315 and mobile app, but don't roll out hidden features we have to discover and debug. Ideally the tone should be similar enough to the detection tone to identify it's a Varia app alert (maybe a friendly/happy tone to indicate "All Clear"). This tone should also be added to Varia compatible head units.