From KDE UserBase Wiki

    Alarm Notification

    In addition to organizing, viewing and editing your events, KOrganizer also provides alarm notification for the events. If you like, KOrganizer reminds you of upcoming events.

    You can set up alarm notifications with the tab Reminder on the New Event window.

    This happens by a simple popup window, by playing a sound file, starting a user-defined program or sending an email to a given address. It is configurable on an event-by-event basis. It is possible to link several alarm notifications with one event.

    You can also suspend alarms and run the alarm notification without running the complete KOrganizer application. This will place a small icon in the system tray of your KDE control panel.