To surely notify that her child has started crying irrespective of the wherever the mother happens to be.

A sampling means 31 samples sounds from sounds collected by a microphone 2 for prescribed time by a fixed time period. CPU 32 compares the sound sampled with a prescribed threshold which has been stored/held in a memory 33 and discriminates whether the sound sampled is by her child's cry or not. If it is her child's cry, a beeper of a subscriber number which is stored/held in the memory 33 is called.