The RadNotification is merely a control that works in the browser, just like any other ASP control. This means that it cannot be shown outside of the viewport of the browser.
It will remain active in a minimized browser as the browser still works and if restored you will be able to see it (again like any other dynamic page).
What I can suggest is that you enable the sound when it is shown
(a new feature in Q3 2011) which will make it more noticeable in the desktop environment.
the Telerik team
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