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A rotary dial phone communicates numbers to the central office by breaking and reconnecting the circuit with a quick series of pulses: a single pulse for 1, two

A rotary dial phone communicates numbers to the central office by breaking and reconnecting the circuit with a quick series of pulses: a single pulse for 1, two for 2, on up to nine for 9 and ten for 0. A longer pause separates the individual digits. So you could either use the dial or tap the hook switch repeatedly in the same sequence. I found it fun to dial numbers by tapping the hook switch. (I guess I am easily amused.) I lived in San Jose in the mid-1990s, and our phones were all touch-tone, but the lines still supported rotary dialing as all phone lines did back then. We had underground utilities that sometimes flooded in rainy weather. During one bad storm our phone was barely usable - when you picked up the phone all you could hear was click after click as the water intermittently shorted out the lines. One day there was a loud and insistent knock on the door: San Jose Police! Open up! I asked if there was a problem and the officers said there had been a 911 call placed from our number but the caller hung up. The 911 dispatcher tried to call back and no one answered, so they were required to come out and investigate. I invited them in and had them listen to the phone, and explained how rotary dial phones work and what must have happened: with all those clicks on the line, at some point there were nine clicks, then one, then one. The officers were relieved that their emergency dispatch was just a technical glitch!

NeedMoreTea 7y ago
Which is actually why emergency numbers were chosen to have 9's in them. 911 in the US, 999 in the UK. Slower to dial and connect, but far less likely to accidentally call via poor wiring or line noise. 0 was often already in use for connecting to the operator in the exchange, so 9 was used. During the 80s or 90s when premium rate chatlines were a new thing, there was a fairly popular urban myth going round: that you could call them free by tapping out the number on the cradle. Course all you're doing is pulse dialling the hard way. You would still be getting the very expensive phone bill. :)
- thombat 7y ago
  Related trivia: New Zealand rotary dialers had the numbers in ascending order, that is zero was in the rest position and nine nearest to the turning stop. The pulse encoder was therefore "ten minus digit", i.e. one pulse when dialling nine, ten when dialling zero [1] - a thread with some crusty old PT&T engineers argues whether this arose to avoid patent/licensing issues or just as a mistake [2] So the emergency number was 111 rather than 999 on the same basis of reducing accidental use, not just from line noise but especially from having the finger slip out partway through the turn of the dial (even with international dialling there was no reason anyone would attempt a number starting with three zeros) [1] https://en.wikipedia.org/wiki/Rotary_dial#/media/File:New_Zealand_Rotary_Telephone.jpg https://en.wikipedia.org/wiki/Rotary_dial#/media/File:New_Ze... [2] https://www.geekzone.co.nz/forums.asp?topicid=171168 https://www.geekzone.co.nz/forums.asp?topicid=171168
  - NeedMoreTea 7y ago
    Fascinating, I never knew that. Seems like the UK GPO sold or licensed handsets overseas too, which I also didn't know. From your link 1, they appear to have used at least some GPO 746's: https://en.wikipedia.org/wiki/GPO_telephones#/media/File:746_telephone_in_ivory.JPG https://en.wikipedia.org/wiki/GPO_telephones#/media/File:746... The 746 was the standard handset just about everyone got in the 1970s.
    - thombat 7y ago
      That 746 photo certainly looks identical to the standard NZ unit, right down to the removable cover in the centre-top (which in big fancy offices was host to an extra switch for some kind of PABX function [possibly just a safer cradle-rest-tap for transferring calls?]. These switches were long rectangles and usually made of clear plastic like a small version of HAL9000's logic blocks - in the days before the BT phone jack reached NZ (around 1987) it was as exotic as anyone's phone could get - we used to salivate over UK electronic magazines and the riot of innovation on display: not just alternative handsets but even directly connected modems rather than acoustic couplers.
      - NeedMoreTea 7y ago
        Aye that switch sounds identical too. There was also some sort of extra switch set that was like a matching base, with 3 or 4 extra switches, that I only ever saw in a movie or two. Both illustrated on that Wikipedia page. Exotic was the arrival of the phone plug. Two phone points in the house and a push button phone, which usually still had a bell. The peak of 80s luxury. By the 90s I wanted a second line as the USRobotics Courier thing was always hogging the phone. :) https://en.wikipedia.org/wiki/GPO_telephones https://en.wikipedia.org/wiki/GPO_telephones
- derriz 7y ago
  The old coin-operated public phones in Ireland (and probably the UK) - the ones with the A and B buttons - were hackable in this way for local calls. I haven't found much on-line about how they worked, but here is a youtube video - https://www.youtube.com/watch?v=SS-tEun2XMc https://www.youtube.com/watch?v=SS-tEun2XMc Although this style of phone was from the 50s or 60s, they remained in use for decades in private settings like schools, hospitals, hotels, pubs and the like right into the 90s. I never paid for a local call from our high school phone by using this tapping technique. But thinking about it now, I suspect the calls weren't "free" - it just meant that the contents of the cash box was not enough to cover the bill the school received every month.
joezydeco 7y ago
And if you ever encountered a phone that had a lock over the buttons, learning to dial by pulsing the hook switch was an excellent bypass. =)

NeedMoreTea 7y ago

Which is actually why emergency numbers were chosen to have 9's in them. 911 in the US, 999 in the UK. Slower to dial and connect, but far less likely to accidentally call via poor wiring or line noise. 0 was often already in use for connecting to the operator in the exchange, so 9 was used. During the 80s or 90s when premium rate chatlines were a new thing, there was a fairly popular urban myth going round: that you could call them free by tapping out the number on the cradle. Course all you're doing is pulse dialling the hard way. You would still be getting the very expensive phone bill. :)

thombat 7y ago
Related trivia: New Zealand rotary dialers had the numbers in ascending order, that is zero was in the rest position and nine nearest to the turning stop. The pulse encoder was therefore "ten minus digit", i.e. one pulse when dialling nine, ten when dialling zero [1] - a thread with some crusty old PT&T engineers argues whether this arose to avoid patent/licensing issues or just as a mistake [2] So the emergency number was 111 rather than 999 on the same basis of reducing accidental use, not just from line noise but especially from having the finger slip out partway through the turn of the dial (even with international dialling there was no reason anyone would attempt a number starting with three zeros) [1] https://en.wikipedia.org/wiki/Rotary_dial#/media/File:New_Zealand_Rotary_Telephone.jpg https://en.wikipedia.org/wiki/Rotary_dial#/media/File:New_Ze... [2] https://www.geekzone.co.nz/forums.asp?topicid=171168 https://www.geekzone.co.nz/forums.asp?topicid=171168
- NeedMoreTea 7y ago
  Fascinating, I never knew that. Seems like the UK GPO sold or licensed handsets overseas too, which I also didn't know. From your link 1, they appear to have used at least some GPO 746's: https://en.wikipedia.org/wiki/GPO_telephones#/media/File:746_telephone_in_ivory.JPG https://en.wikipedia.org/wiki/GPO_telephones#/media/File:746... The 746 was the standard handset just about everyone got in the 1970s.
  - thombat 7y ago
    That 746 photo certainly looks identical to the standard NZ unit, right down to the removable cover in the centre-top (which in big fancy offices was host to an extra switch for some kind of PABX function [possibly just a safer cradle-rest-tap for transferring calls?]. These switches were long rectangles and usually made of clear plastic like a small version of HAL9000's logic blocks - in the days before the BT phone jack reached NZ (around 1987) it was as exotic as anyone's phone could get - we used to salivate over UK electronic magazines and the riot of innovation on display: not just alternative handsets but even directly connected modems rather than acoustic couplers.
    - NeedMoreTea 7y ago
      Aye that switch sounds identical too. There was also some sort of extra switch set that was like a matching base, with 3 or 4 extra switches, that I only ever saw in a movie or two. Both illustrated on that Wikipedia page. Exotic was the arrival of the phone plug. Two phone points in the house and a push button phone, which usually still had a bell. The peak of 80s luxury. By the 90s I wanted a second line as the USRobotics Courier thing was always hogging the phone. :) https://en.wikipedia.org/wiki/GPO_telephones https://en.wikipedia.org/wiki/GPO_telephones
derriz 7y ago
The old coin-operated public phones in Ireland (and probably the UK) - the ones with the A and B buttons - were hackable in this way for local calls. I haven't found much on-line about how they worked, but here is a youtube video - https://www.youtube.com/watch?v=SS-tEun2XMc https://www.youtube.com/watch?v=SS-tEun2XMc Although this style of phone was from the 50s or 60s, they remained in use for decades in private settings like schools, hospitals, hotels, pubs and the like right into the 90s. I never paid for a local call from our high school phone by using this tapping technique. But thinking about it now, I suspect the calls weren't "free" - it just meant that the contents of the cash box was not enough to cover the bill the school received every month.

joezydeco 7y ago

And if you ever encountered a phone that had a lock over the buttons, learning to dial by pulsing the hook switch was an excellent bypass. =)