http://www.purl.org/tcl/home/man/tcl8.4/TkCmd/bell.htm
bell ?-displayof window?
This command rings the bell on the display for window and returns an empty string. If the -displayof option is omitted, the display of the application's main window is used by default. The command uses the current bell-related settings for the display, which may be modified with programs such as xset. This command also resets the screen saver for the screen. Some screen savers will ignore this, but others will reset so that the screen becomes visible again.