How did they trace phone calls in the old days?

I was reading a detective novel written back in the '40’s and at one point the hero had a phone call traced. Well, today that wouldn’t be such a big deal. What with all the modern electonics we’ve got, it’s not much of a surprise that a call can be traced to its source in a matter of minutes or even seconds.

But back then they used actual switchboards. (When was the last time you saw a switchboard?) Connections had to be made by hand by a human operator, often more than once. Long distance calls could involve any number of switchboards. Placing a long distance call overseas was a major project; you pretty much had to plan your whole day around it. (Let’s not even talk about the bill.)

So I’m wonderin’. Just exactly how did they trace calls? Did they contact every operator involved in making the connection? How did the operators know which call an investigator wanted? Did she (operators were usually female)keep a log of every connection she made or something? In old gangster movies, you’ll often hear the cliche, “Keep him on the line so we can trace the call.” Was it possible to trace a call only when the connection hadn’t been broken yet?

Somebody help me out here so I can get back to work. :smiley:

They ran around looking for a light on the big circuit boards in the back room to find where the connection went. As you can see, it wasn’t very practical or fast.

Just a note - local calls at that time were mostly made by automated switches - a mortician named Strowger invented the first electromechanical switch in the 1890’s. That’s why you could actually just dial a local number. Operators were required for long distance before DDD arrived in the fifties, but the basic reason was the lack of a uniform numbering plan which would allow you to sensibly dial a number outside your exchange so that switches could be set up to automatically route it. We’ve had a bunch of threads touching on this topic.

As for tracing a call, it would be feasible with an electromechanical switch by simply noting what is currently connected to what, as long as the call stayed up (probably a germ of truth in that “keep them on the call” scenario).

How easy that was, or what provisions were made for it in the common switches of the time, I don’t know. Somebody else probably does.

Although devices had been invented for logging call traffic on electromechanical switches, I doubt that they kept individual records of local calls.

My dad had some experience of call tracing in the UK customs drug squad.

It required forward planning because you needed somebody in each exchange the call passed through to trace it through the switches. You could monitor the call by plugging a handset into the connection. Obviously you would need some idea of the call origin before you started and you had to try and keep the line open long enough to complete the trace.

The idea that you could ask for a trace after the call was complete was just hollywood BS.

handy said

You said this in jest, right?