During the mid 1900’s telephone companies where doing their best move away from having operators connect each individual call. As phone systems spread throughout the nations the system just didn’t scale well.
The original process of picking up the receiver and asking the operator to connect your call was pushed out. The solution that had gained traction was tonal commands. Beeps and boops from telephones would instruct central routers on how to handle a call, allowing a home phone to issue commands.
Like most people, I hadn’t really thought much about how my home phone worked, until one day a friend showed me that it was possible to dial numbers by clacking the “hang-up” button in quick succession.
So to dial 911:
Tap the “hang-up” button nine times, wait a moment, tap once, wait a moment, and once more. Boom, you are talking to dispatch.
This successive tapping is the same type of signal that rotary phones would use to send numbers to the switchboard machines. As the spring loaded wheel would return to its places it would send successive taps.
