When I was a little kid I remember that my parents gave me my grandparents’ old discarded telephone to play with. It was one of those phones that had an old fashioned electro-mechanical ringer inside it.
I took it apart and examined the innards. What I saw was very educational.
There was a metal springy clapper that was designed to hit a bell. When it hit the bell, that would connect an electric circuit that would activate an electromagnet. The electromagnet would then attract the clapper which would pull back toward the electromagnet. When that happened, the electric circuit became disconnected, which turned off the magnetic attraction.
The clapper would then fly back toward the bell striking it again. This would repeat over and over again as long as the ringing was supposed to continue.
Even today, when you hear a classic ringtone, you were hearing a re-creation of this electro-mechanical mechanism.
What was wonderful about this was that even I, a small child, could see this and trace through and understand the principle. Sadly, that is no longer the case with today’s all-electronic mechanisms.