# How do those "retro" handsets work? **URL:** \ **Category:** Factual Questions\ **Created:** [August 28, 2013, 4:23pm UTC](https://boards.straightdope.com/t/how-do-those-retro-handsets-work/667411 "2013-08-28T16:23:14Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![keno](https://avatars.discourse-cdn.com/v4/letter/k/f9ae1b/32.png) [@keno](https://boards.straightdope.com/u/keno)\ **Post date:** [August 28, 2013, 4:23pm UTC](https://boards.straightdope.com/t/how-do-those-retro-handsets-work/667411/1 "2013-08-28T16:23:14Z")
They look like the handsets from old desk top phones – speaker and receiver in one unit with cord. The “retros” plug into your cell phone’s headphone jack. Since the headphone jack is designed to transmit a signal, how can what you speak into the handset get to the cellphone to be transmitted? ---
**Author:** ![ryanl](https://avatars.discourse-cdn.com/v4/letter/r/b487fb/32.png) [@ryanl](https://boards.straightdope.com/u/ryanl)\ **Post date:** [August 28, 2013, 4:26pm UTC](https://boards.straightdope.com/t/how-do-those-retro-handsets-work/667411/2 "2013-08-28T16:26:37Z")
> [@keno](#): > > They look like the handsets from old desk top phones – speaker and receiver in one unit with cord. The “retros” plug into your cell phone’s headphone jack. **Since the headphone jack is designed to transmit a signal** , how can what you speak into the handset get to the cellphone to be transmitted? In my phone, the headphone jack both transmits and receives, as I have a corded headset that includes a microphone. ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [August 28, 2013, 4:32pm UTC](https://boards.straightdope.com/t/how-do-those-retro-handsets-work/667411/3 "2013-08-28T16:32:02Z")
Most cellphones have [TRS or TRRS](http://en.wikipedia.org/wiki/TRRS#Mobile_phones) jacks which can provide an audio and mic signal, and also a control signal in the latter case. ---
**Author:** ![keno](https://avatars.discourse-cdn.com/v4/letter/k/f9ae1b/32.png) [@keno](https://boards.straightdope.com/u/keno)\ **Post date:** [August 28, 2013, 5:08pm UTC](https://boards.straightdope.com/t/how-do-those-retro-handsets-work/667411/4 "2013-08-28T17:08:13Z")
How can you tell if your phone has a TRS or TRRS jack? ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [August 28, 2013, 5:12pm UTC](https://boards.straightdope.com/t/how-do-those-retro-handsets-work/667411/5 "2013-08-28T17:12:11Z")
Look up the specs for your model online. Or try a TRRS accessory and see if it works. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [August 28, 2013, 5:36pm UTC](https://boards.straightdope.com/t/how-do-those-retro-handsets-work/667411/6 "2013-08-28T17:36:54Z")
Yeah, IIRC the iPhone comes (came?) with an accessory earbuds that included a tiny microphone that looked like a small thin long bead on the headset cord, and eneded up near your throat. it also has a volume control. Plus, in Camera mode with the new iOS, using the volume controls will take a picture - either the volume buttons on the side or the volume control on the headset. Google image for “iphone headset” and you will see too many examples. ---
**Author:** ![dstarfire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dstarfire/32/5762_2.png) [@dstarfire](https://boards.straightdope.com/u/dstarfire)\ **Post date:** [August 28, 2013, 6:08pm UTC](https://boards.straightdope.com/t/how-do-those-retro-handsets-work/667411/7 "2013-08-28T18:08:42Z")
The “headphone” jack is actually a standard socket size with connectors arranged along axis of insertion. That socket can support a monaural headphone (2 lines), stereo headphones (3-4 lines), or some more complex interface with 4 or more lines. A monaural headphone/earpiece will work just fine in a stereo socket, and a stereo headphones will work in a monaural socket. The reason this is possible is because the lines are subdivided as you add more, so stereo headphones would have the left and right signalling lines in the same space the monaural headphones have a single signalling line. As long as you’re sending data in some of the same space headphones the other device is expecting it, things generally work just fine. I’m sure there are some complications I’m missing and additional steps, but that’s the general idea. ---
**Author:** ![Ellen\_Cherry](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ellen_cherry/32/3600_2.png) [@Ellen\_Cherry](https://boards.straightdope.com/u/Ellen_Cherry)\ **Post date:** [August 28, 2013, 6:33pm UTC](https://boards.straightdope.com/t/how-do-those-retro-handsets-work/667411/8 "2013-08-28T18:33:01Z")
I will chime in, even though I don’t know how they work, that I love mine. I end up talking to my girlfriends in distant cities for hours sometimes, and if I lay down, the noise-cancelling whatever at the top of the iPhone gets covered up and they can’t hear me. (At least that’s how it was explained to me what’s happening.) Now using the retro handset, I can yack and loaf in comfort. Plus not melt my brain. ---
**Author:** ![LawMonkey](https://avatars.discourse-cdn.com/v4/letter/l/d6d6ee/32.png) [@LawMonkey](https://boards.straightdope.com/u/LawMonkey)\ **Post date:** [August 28, 2013, 7:00pm UTC](https://boards.straightdope.com/t/how-do-those-retro-handsets-work/667411/9 "2013-08-28T19:00:29Z")
> [@dstarfire](#): > > The “headphone” jack is actually a standard socket size with connectors arranged along axis of insertion. That socket can support a monaural headphone (2 lines), stereo headphones (3-4 lines), or some more complex interface with 4 or more lines. Pointless nitpick: Assuming we’re talking about the same “lines”, i.e., the painted/enamel ones, monaural have 1, stereo have 2, and every integrated mike stereo jack I’ve seen has had 3. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [August 29, 2013, 6:46am UTC](https://boards.straightdope.com/t/how-do-those-retro-handsets-work/667411/10 "2013-08-29T06:46:02Z")
Are those jacks standardized? I bought a cell phone, but they didn’t have a head-set (including microphone) for it. So I went to the nearest big-box office supply store and got a perfectly generic headset there. ---
**Author:** ![si\_blakely](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@si\_blakely](https://boards.straightdope.com/u/si_blakely)\ **Post date:** [August 29, 2013, 7:24am UTC](https://boards.straightdope.com/t/how-do-those-retro-handsets-work/667411/11 "2013-08-29T07:24:12Z")
> [@Senegoid](#): > > Are those jacks standardized? The physical (TRRS) specification is standard, but the way those connectors are used [varies](http://en.wikipedia.org/wiki/TRRS#Mobile_phones). Accessories for one phone may not work correctly on another. For example, iPhones provide a DC offset on the mic line that can power some accessories - other manufacturers do not. Signalling (i.e. buttons and other controls on the headset) may be provided by audio frequency signals (hi or low frequency) on the mic line that software/DSP firmware on the phone has to catch and respond to. So YMMV. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [August 30, 2013, 2:23am UTC](https://boards.straightdope.com/t/how-do-those-retro-handsets-work/667411/12 "2013-08-30T02:23:48Z")
> [@LawMonkey](#): > > Pointless nitpick: Assuming we’re talking about the same “lines”, i.e., the painted/enamel ones, monaural have 1, stereo have 2, and every integrated mike stereo jack I’ve seen has had 3. The enamel is the insulator between metal contacts. One line, two metal contacts, mono speaker. Two lines, 3 metal contacts, stereo speakers (L signal, R signal, common ground) Three lines, 4 metal contacts, a microphone also with common ground. The pieces are arranged, I imagine, so a normal stereo jack will not cause problems in a iPhone that might also feed a microphone.