If you are the sort that like to set your watch so that it chimes on the hour, you should probably know that you can set you your Mac to do the same thing. Go to the System Preferences tab, select the Date & Time panel, and then click on the Clock tab. At the bottom of the panel is an option to "Announce the time". You can opt to have the time announced on the hour, the half hour, or the quarter hour using any of the computerized voices that are available on your Mac.