In some cases you might get confused which control you need to use - RadDesktopAlert or RadAlert.
RadAlert (Figure 1) is a modal dialog window that gets visualized during user interaction with the interface. It prevents the user from accessing the rest of the program's interface until it gets closed - the UI behind RadAlert becomes inactive.
Figure 1: Alert
If you need to display a notification for a short period of time RadDesktopAlert (Figure 2) is what you need. It is displayed as a small notification window on a predetermined location and gets automatically closed after the elapsing of specific duration.
Figure 2: DesktopAlert