Flash screen for Slack alerts

Question

I have enable the option to "Flash screen when an alert sound occurs" under Accessibility setting in System Preferences.

It works successfully with many apps such as Microsoft Outlook but not with Slack. How can I get the screen to flash when I receive a Slack notification?

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Further information:

It looks like Slack uses the native notification interface as you can control the notification type under the Notification Centre settings:

Answer 1

From an email with Slack support:

The MacOS flash screen setting is based on the system default "alert" sound. If an application uses the system default "alert" sound, the screen will flash. Since Slack never plays the system default sound, we'll never flash the screen.

For now, I'm afraid this means there is no way to flash the screen when Slack receives a notification. That said, I've let the team know that this is something you'd like to see in the future.

This was written on the 16th May 2019. Slack v3.3.8