Fun Fact About Mac OS X

I’m no sure, but I think that the below indicates that if you hit the precise turning of the hour and you have the time in your shell config, you get to see “DING!” on the command line.

[4:58pm][artlung@The-iBook:~]:
[DING!][artlung@The-iBook:~]:

I wonder if this is common to all unices? And I wonder if my interpretation is correct?