On Saturday, 20 June 2020 15:43:41 UTC+1, Dave W wrote:
No they don't. You press the button and it goes ding, then relase the
button and it goes dong. Unlike 'digital' bells which play the same
tune however the button is pressed, you can get an idea of how
desperate the caller is by the gap between ding and dong.

I wired up one as a telephone ringer. The ding-dong superposed on the British ringing cadence gives

ding...dong-ding...dong...............ding...dong-ding...dong...

Well, it amused me at the time, and the neighbours appreciated it more than the Swedish foghorn I also had.

Owain