The reminder sound is not global to the Windows CE operating system, and is specific to the Calendar and Tasks portions of Pocket Outlook. To change the sound in either application select Tools/Options and then tap on the Bell button. Next tap on Reminder Options... and finally select the sound that you want in the drop down list. The default sound for either is Alarm1. You might want to make the default sound for appointments different from tasks so that if you hear the alarm you will quickly know whether it is for an appointment or task.