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  The real-time clock's alarm feature generates an interrupt at a specific
  time. To take advantage of this feature, you must create an interrupt
  handler that performs an action when the alarm interrupt occurs. You can
  even make this action independent of other programs by leaving the
  interrupt handler resident in memory with a DOS
  Terminate-and-Stay-Resident service. (See Chapters 16 and 17.)

  The ROM BIOS provides a set of services through interrupt 1AH that give
  you access to the real-time clock's alarm feature. See Chapter 12 for
  more details.