You need to start with a try. First tackle the trigger point, how much noise would make
the OpAmp turn on buzzer. Hint OpAmp 2 is being used as a comparator, what makes
a comparator change its output V ?
Could be: The teacher's notes have become the students notes; without passing through the minds of either.
“The mediocre teacher tells. The good teacher explains. The superior teacher demonstrates. The great teacher inspires.” – William Arthur Ward
The great ones; I call Sensei.