"John R Weiss" wrote

Squawk 7700 briefly (15 seconds?) to get the attention of ATC, and
to give some notice of your intention to exercise your PIC emergency
authority to "bend" the regulations.

John, this used to be true way-back in the old days when only 7700
rang the bell, but several years back, they re-wrote the software
so that now, 7500, 7600 and 7700 all ring the bell.

Bob Moore