This is a quick tip if you want a more visual way of being notified when you get a notification, message or alert within Mac OS X. Along with the audible beep you can get the screen to flash for a brief second. This flash originates from the outer corners of the screen and is a subtle visual reminder that you have something to do. It occurs infrequently but is useful when it does appear.
To get the screen flash open System Preferences and select the Accessibility preference pane. Under the hearing, audio, option enable the check box “Flash Screen When Alert Occurs” . You can test the option with the button. Its subtle but informative.
You can test the alert with the button. Turning if off is a simple case of deselecting the check box.