If you’ve ever watched a movie set in the early 1900s, you’ve almost certainly seen someone making a call on a phone that has an earpiece on one side and a distinctive crank on the other side. While the earpiece makes perfect sense, the purpose of that crank can be confusing, even if you grew up in the era of landlines with coiled wires. You might think the crank was used to power the phone, but that’s only half the truth. Back then, the crank was actually the most important part of the entire device, because it generated electrical pulses that alerted your local telephone company to forward your call.
We must remember that when telephone technology was in its infancy, the infrastructure we had today was nowhere near comparable. Telephones had no dials or buttons, and you couldn’t make a call on your own; you needed an operator to connect two phones together. This crank served as an alert to your local operator, letting them know that someone was trying to make a call and to get on the line quickly. This may seem like an outdated and useless technology today, but it was quite revolutionary at the time.
The cranks alerted the operators that someone was trying to call
The classic crank telephone had several key differences from modern landline telephones, chief among them being the conspicuous absence of dials or buttons. The first telephones were less like the telephones we have today, which can freely call any number, and more like a pair of tin cans tied with string. To initiate a call, the caller would turn the crank to alert the local telephone operator, who was located at a telephone exchange, and the operator would ask you who you would like to connect to.
When the telephone crank was turned, it turned a small magneto generator hidden inside the device and generated an electric current. This current would trigger an alarm bell at the telephone exchange, a rather distinctive forgotten technological sound, to inform the operator that someone wanted to make a call. Once they had the line, you would tell them who you wanted to call and they would connect you. And when you finished your call, you would turn the crank again to let the operator know you were done, and they could close the line.
