You can be notified of successful and failed faxes by email or text - in the extension notification settings.
To have a sound on your computer or mobile notify you of a failed fax, you would have to install a 3rd party app that monitors your email or text and triggers a sound alarm based on content.
For faxes taking a long time (ie. RC service is running slow and/or the recipient's line is busy and the auto-retry of 3 times is being implemented) you could only monitor this with a more specialized 3rd party app that would either:
- send your fax by email to RC and then monitor the time before a notification reply arrives (or doesn't arrive) and then alarms on the duration you setup
- monitor outgoing faxes with an app that accesses the RC API to monitor your actual faxes
Bottom line, is that with the RC tools and settings, you cannot do this. But technically it can be done with 3rd party apps/services.