Ask for the old-fashioned bell for class.

In the primary school where I used to teach, I smashed a steel plate with a hammer and rang the following bell:

Class: Dangdang Dangdang Dangdang Dangdang Dangdang

Class dismissed: dang-dang-dang.

Later, when I entered the county primary school, the bell became a bell:

"Rinrin Bell ..."

I think this kind of clock is the closest to ancient times for our teachers of the older generation.