Rotary Telephone Trick?
November 21, 2017 1:38 PM   Subscribe

I started reading "Secondhand Time" after seeing it recommended in another ask, and I'm curious about a "trick" that involves a rotary phone. The trick was "so that the KGB agents who tapped our phones wouldn't be able to make anything out"

The passage in question describes it like this: "You turn the dial to the end - old telephones had little holes for numbers that you could turn - and then you stick a pencil in it so that it locks... You can hold it down with your finger, too, but your finger gets tired... You probably know that one?"

I don't know that one. I am familiar with rotary phones and I can picture myself doing this, but I don't know what it would actually accomplish. Does it actually do anything?
posted by one4themoment to Technology (9 answers total) 5 users marked this as a favorite
Turning the dial sends a pulse down the line to the central office and starts the circuit which decodes the pulses from the rotor. This disables the line for incoming calls, and presumably for listening on the normal, unattached line. The line is busy and can't be eavesdropped. Wiki for more.
posted by blob at 1:47 PM on November 21, 2017 [1 favorite]

It does nothing. In fact, rotary phones don't "dial" until you *release* the dial, so swiping to a particular number doesn't do anything that the phone system could sense.
posted by scolbath at 1:48 PM on November 21, 2017 [2 favorites]

It doesn't do anything in terms of dialing a number. It sounds like this is talking about doing this while speaking. (I don't know what it does either, but I just think it would be helpful to clarify exactly what is happening).
posted by FencingGal at 1:59 PM on November 21, 2017 [1 favorite]

The reason it doesn't do anything when dialing a number is that when a phone goes "off-hook", a circuit is set up with the central office - and you get dial tone. "Dialing" (or hanging up for that matter) occurs when you break the circuit for a requisite amount of time. You can actually dial an old POTS home by rapidly pressing the switch-hook at the right rate. Moving the dial on the old rotary phones just primes a spring so that when the dial is released, it actuates a switch the correct number of times at the right rate.
posted by scolbath at 2:08 PM on November 21, 2017 [6 favorites]

This sounds like an idea the KGB would want to promote, both as a joke (thinking about all the people holding their dials against the spring) and as a way to make people think a communications medium was more secure than it was, and therefore not seek out alternatives.
posted by straw at 3:34 PM on November 21, 2017 [1 favorite]

Here is how the actual switching system worked, at least in America, I see no reason to believe Soviet technology would operate on wildly different principals.
posted by Dr. Twist at 3:44 PM on November 21, 2017

I still have a rotary phone hooked up to my landline, and I just tried this ... if you do this when on a call from the rotary phone the person on the other end of the line can hear all the sounds from the rotary phone but you can’t hear the person on the other end of the line. So this would have the exact opposite effect.
posted by fimbulvetr at 5:52 PM on November 21, 2017 [3 favorites]

A little off topic, but possibly of interest would be this Atlantic article about a great book "Exploding the Phone" which gets into the nuts and bolts of the history of phone hacking.
posted by eglenner at 9:25 PM on November 21, 2017

I'm pretty sure I've seen this in a film or two (Gorky Park maybe?).
The presentation of it led me to understand it this way:
- a desk telephone handset, with its included microphone, is a 'bug' on every desk I can listen through, providing
- I can manipulate the 'hook' function on each of the phones in an office building or disable the 'hook' switch entirely, such that 'hanging up' does not cause a disconnect, but instead leaves it in an open-line status
- then I can sit at the switchboard and listen through the microphone of any/every telephone in the building, simply by connecting to that extension's open line. Two people talking across a desk, me listening through the handset on the desk between them as if I'd been called and they left the phone off the hook between them.

One would defeat this by _partially_ dialing a new call but not completing; therefore taking the unit out of open-line status, but not re-engaging the line by making a new connection. In this case, dialing a 1 but holding the rotor partway through so the phone is in limbo - not an open line, not dialing #1...

[The modern version of this might be to hack a mobile phone so that it _appears_ to hang up but never actually disconnects. Then all I have to do is call your phone and get you to answer and hang up (but not really, hacked); then I'll be able to listen through your mic. Kinda like a butt-dial listen-in, but I'm dialing _your_ butt.]

So say you work in Lubyanka, or in Stasi HQ or wherever. You and everyone else assumes that all the desk phones are tapped in this manner, that there are um, 'political officers' listening through the handsets of all the phones.
I call you into my office because I've got a line on some contraband bluejeans that I want to trade for your contraband jazz records. Before speaking, I give you a pointed look, then half-dial my phone and stick a pencil in the rotor. Now we understand each other.

Even if this telephone trick is not actually effective, and/or there's another microphone in the potted plant anyway, it's a signal with a meaning. That's probably why it's in your book or the movies I've seen it used in.
posted by bartleby at 12:45 AM on November 22, 2017 [3 favorites]

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