Int 4A  C - System - User Alarm Handler                                    [B]

Desc:  This interrupt is invoked by the BIOS when a real-time clock alarm
     occurs; an application may use it to perform an action at a
     predetermined time.

Note:  this interrupt is called from within a hardware interrupt handler,
     so all usual precautions against reentering DOS must be taken

See Also: INT 1A/AH=06h