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Show HN: I built an intercom for my 6 yo to keep us connected during quarantine (chordata.cc)
181 points by daylankifky 9 days ago | hide | past | favorite | 123 comments

Back in the days of landlines, all corded phones in a house effectively acted as an intercom system. Two or more users could pick up handsets, and their voices would be broadcast to one another.

This worked even while on a call. If you had siblings (or snooping parents), you learned to be alert for the click sound during a call which indicated that someone else had picked up a handset and was now eavesdropping.

When I was a kid, a single phone line was shared between 3 or so homes. If you picked up the phone and heard the neighbors talking, you said sorry and hung up and waited for a while before trying again.

When the phone rang, the ring was morse code for the letter matching the intended home. Our number was 4045D, so our ring was long, short, short.

My dad grew up with "party lines", as they were called back then, with over 10 lines.

The number of rings determined who the call was for and anyone (even in different houses on the same line) could pick up and listen in or talk on the line.

Some systems used phased ringi g so only the correct phone would ring, but I'm having trouble finding details.

That last party line in the US was taken out in 1991! https://www.numberbarn.com/blog/phone-history-party-lines/

It's amazing to think that even switchboard operators were a thing long into the 1980s.

There wasn't an operator, though. It's a "party line". The same wire pair is connected to multiple subscribers. My grandmother had one of these in the early 80s.

I don’t know why exactly but I genuinely love this image - thank you for sharing. It makes me nostalgic for a time I never even experienced

Very interesting, when and where was this?

In New Zealand in the late 1960s.

My Kindergarten class in the late 80's had a phone system between play areas for the kids to use. The system was built using some old phones and lantern batteries for power. As a small child it was really neat to pick up the phone and talk to someone on the other side of the classroom.

I recall trying to build a can-and-string phone. There's something magical about remote communication, especially if it's completely analog - just the power of your voice.

Wow, that's so cool!

How old are we all now that we talk about this as if it where ancient stuff? I remember my grandfather tell me about how they used to gather around the radio to listen to the radio shows (or whatever these were called...). Incredible how something like a land line phone is now a thing of the past (not so distant!). In Argentina it was not until the lates nineties that most people have access to a phone at home. Now everyone has a mobile phone. The power of technology evolving at exponential rate I guess!

> In Argentina it was not until the lates nineties that most people have access to a phone at home. Now everyone has a mobile phone. The power of technology evolving at exponential rate I guess!

And there are places elsewhere in the world (for example, some African countries) that skipped completely landlines because mobile phones require much less pervasive infrastructure to work properly.

At least in Argentina it was not because of the infrastructures, it was because of the telefonica monopoly. Once deregulated, private companies came and in few years most middle class families could have a land line, cable tv and Internet.

I'm only 35, but even when I was young (90s) the rotary phones we had were considered dated technology. (Pushbutton phones were more typical; cordless phones were the new thing.) Northeast US.

My mother still uses those rotary phones, BTW. Somehow the telco in her area still supports click-dialing. Incoming calls are great, every damn phone in the house rings simultaneously; sounds like a fire alarm.

Where I grew up the phone lines weren't very well isolated, so if lightning struck within a few mile radius the phone would ring before the thunder arrived.

I was thinking that too, but at the same time I'm glad those days are over. I don't miss that at all.

I was thrilled that my ISP/Cable company didn't try to sell me their "TV and Phone" bundle because they understood the absurdity or could tell by my voice and interests that I wouldn't be interested or the target audience.

I’m also very happy. I was reflecting about the speedy nature of tech changes. Now no one “remembers” land lines AF of these were from there 50s or before (I guess they are?). What’s next? Currencies? Over the air tv? Gasoline? What things that we take for granted will disappear, obsolete 20 years from now?

On the other hand, if your ISP was crap, you could easily pick a new one. If they were all crap, you could start your own with a t1 to connect to the internet, and another t1 (or less) to answer calls.

If your phone company was crap, you were kind of stuck, but they usually weren't too bad.

I still have to pay for a phone line (UK, Virgin Media), as it's cheaper, but there isn't even a phone jack in the house now.

I used my very first paycheck from my very first job as a teen to get my own phone line set up in my room. Mostly so I could use the internet (dial-up at the time) without tying up the phone line, but also so I could avoid my siblings snooping on my calls.

It also worked out because my parents could just call me when it was time for dinner.

That must have been a big paycheck!

Getting connected the first time is cheap. It's the bill that comes for the second month for all those minutes that gets you!

Mid 90s you'd only pay $15 a month for basic service in some places. Probably less for second lines.

ISPs were spottier. I knew some people with T1s paid for with weekend jobs, but some could barely scrape 56k costs.

Where I lived, the minimum wage was about three bucks.

My first job was washing dishes at a cafe for about 30 hours a week for minimum wage (which in my state at the time was around $5 an hour). I also got a portion of the tips made by the front room staff (usually a few bucks a day). So as a teen who wasn’t expected to pay rent or anything it was a pretty decent amount of money!

I also installed the phone line tap in my room myself, so initially I just had to pay for them to come out and turn on the line via the hookup box outside. I think it was like $50 for the initial setup and I saved $100 by running the tap myself.

In fact you had to be on a call, otherwise the dial tone would drown out your voices.

You could dial just 1 digit and the dial tone would stop. You could tap the off switch to do pulse dialing too (a bit like morse code).

I forget the exact details, but as a kid, I'd tap the switch and hang up the phone I think and then that would cause the phone to ring in the house so that you could "call" somebody.

I remember you could dial your own number, and it would call you back with a recording.

I also remember dialing a three digit number (maybe 118), and an automated voice would reply with the number you are calling from.

In the UK bitd (~1980) the test number was 174. It just rang you back when you hung up. There was no message. The exchanges weren't that sophisticated.

What country was this in? I distinctly remember dialing my own number resulting in nothing but a busy signal.

On mine, it was 981 followed by the last 4 digits of my phone number that would result in a "callback," and a constant tone would play when you answered.

I’ve also (a decade ago) called my own number (a cell line) and it gave me my voice mail as if I had just “speed dialed” “1”

You can still do that on hard-wired AT&T land lines. The hardware at the CO end supports it, and it's still enabled.

Yep, I forgot this step.

I had a friend who had an intercom system in their home — they were not uncommon in suburban, mid-Century modern homes in the day.

Unlike using multiple telephones, the recipient did not have to be on the line — you could broadcast "Dinner's ready!".

I think I need an intercom as my teen daughters spend all their time up in their rooms....

I know they're unpopular on HN, but smart speakers are an easy off-the-shelf solution for this, saying "Hey Google, broadcast 'dinner in ten'" will cause all the Home/Nest/whatever they're branded this month units to say "Broadcast from $USER, dinner in ten". Same syntax works for Alexa.

I guess I still like the lower-tech, "wired" intercoms.

you can also broadcast to a specific room with google home. "hey google , broadcast to (PERSON ROOM)." you just have to add that GH to a room by that name in the Home app.

This ended before landlines did - When I was growing up it was common that you only had one phone line connected (or only one period). Multiple handsets were handled by a base station which used some form of wireless transmission. If the handset hadn't been used to pick up a call, it wouldn't play back the signal (I'm sure given the time period, it was still being broadcast, and unsecured, but it was still a bit more involved to listen in than just picking up the other handset).

That's what I meant by "corded phones". You are of course correct this would not work with a single set of cordless phones.

You are right, cordless phones definitely broadcast with no encryption of any sort. There was a recent HN thread about how radio receivers were banned from receiving the band these phones used because of this.

We used to do this by calling the house number, hanging up, and picking up both ends on the ring.

Works just fine with a 6-piece Panasonic DECT set from Costco. It's technically a landline phone, but you don't need to plug it in, or can use one of these Chinese Ethernet-to-phone-line boxes.

While this could be the case, it was not always the case for landlines.

An intercom/telepresence for kid is a nice idea, and sounds fun to build.

Especially when building things with impressionable kids, I'd like to encourage people to try to figure out how to build things while minimizing unnecessary third-party dependencies, and secondarily by judicious selection of complexity.

For example, maybe using WiFi and a SoC board with stripped-down Linux, and software to make them talk to each other over the LAN. Or maybe a microcontroller board with a WiFi module in ad-hoc mode. Maybe coded in one of the education-oriented programming tools that the kid will be able to start using soon. Or maybe old-school analog circuits over a pair of copper.

(Or, if you want the kid employable this year, maybe that means gluing together 10 different SaaSes that snoop on your traffic, building a Kubernetes cluster in the cloud for um reasons, using 3 Web frameworks, pulling in 1,000 NPM dependencies, and throwing in half a dozen third-party trackers. :)

https://relaygo.com/families is a great solution if you don’t want to home brew it and don’t mind a monthly fee for the cell service.

No affiliation, just a customer/user.

Thanks for the shoutout! Product Manager at Relay here. We also have an API if you want to build your own solution with it. relaypro.com/api & api-docs.relaypro.com

Your api is awesome btw. If QI charging support isn’t on the roadmap for the hardware, any chance it could get in your backlog? :)

Hey thanks! We support QI charging for our Relay+ devices (https://relaygo.com/relay-plus#pip-relay-plus)

We have a free version called Squawk over at https://www.squawk.to

I think the stripped down hardware is quite an important part of the offering.

For anyone interested in push-to-talk/intercoms we built a free tool at the beginning of quarantine last year called Squawk - https://www.squawk.to

Looks intriguing, but from the website I can't really tell what it does/doesn't do. Maybe a quick youtube video would help make this concrete? For me, the question is: if I put this on an old smartphone and put it in my kid's room, can I/she use Siri to send each other message? Or do we have to separately open the app, wait for it to load, and then say the message?

Interesting. How do you make money on it?

When something is free it usually is paid for by selling my data, as the free-tier of a paid product, or the owners haven't figured out how to make money on it and are hoping to figure that out later.

We don't but it helps with marketing and has synergies with other paid products

Most of the traffic is P2P. We operate a couple of geo distributed relays for NAT'd traffic. But everything is 100% e2e encrypted thanks to webrtc.

It's mostly a tool for us and something that helps sell our other products, but we decided to split it out as a separate app so that it could be used independently. All we collect is a name and email, and even those can be pseudonymous.

The site seems to be down?

Something like WP Super Cache would help a lot during traffic spikes: https://wordpress.org/plugins/wp-super-cache/

Interesting choice to use Telegram voice messages for the intercom. I don't think I would've personally trusted Telegram's unencrypted, third-party system to store messages intended for children, though.

I've theorised about such a system myself, though I'd go with live voice-chat through something like a private SIP server (with multiple channels and/or a broadcast mode). With a bit of setup, you could probably integrate Android's native SIP dialer and the various other desktop SIP tools into the system and connect to a channel remotely.

My underengineering method would be to just run a Mumble server on the LAN and join everything to it.

This also means you can do things like turn certain intercoms one-way, or certain ones into priority speaker broadcast mode in software client remotely.

The website appears to be down. Having said that...

I may not be remembering this correctly, but didn't most mobile phones also have a walkie-talkie feature built-in in the 90's ? I don't think any have that now.

In the US it was mostly Nextel phones that had the push-to-talk feature, which allowed walkie talkie-like communication. (one to many, no cost, etc.)

from https://en.wikipedia.org/wiki/Nextel_Communications

"Nextel's iDEN network offered a then unique push-to-talk "walkie-talkie" feature in addition to direct-dialed voice calls."

I'm not sure if I'd feel the same today, but back in the early 2000s, that was such a great feature. I was pretty sad when our company decided to move from Nextel over to a traditional carrier without push-to-talk.

It was super useful to track people down when you were trying to coordinate. I remember on 9/11 in NYC, my nextel phone was the only one that was working in washington square park. I had a line of people waiting to use it to call loved ones to let them know they were okay.

As a high schooler who only had Nextel phones for the cool factor, I will never forget the constant anxiety in the back of my mind that I'd have the phone off mute and one of my friends would chirp me when I'm around my parents with something I'd rather they not hear.

Ha! I can imagine that. We occasionally had that issue, but mostly my group of friends and coworkers shared some basic rules for using the push-to-talk. E.g. no pushing the button and then just saying something, unless you were already talking back and forth; the first chirp was always an empty chirp. If the other party was available, then they could respond. Stuff like that. I can see that with some raunchy high school friends it could get pretty awkward.

I remember Nextel phones having that cool feature (and a distinctive chirp sound)...but don't recall other phones having that...THen again, i always did have cheapy phones back in the day. It is surprising why walkie-talkie-like features aren't more popular nowadays...Then again, maybe messaging apps might fit enough of the original need.

I haven't looked into this article, but over Christmas we went to visit my Grandma at her nursing home, which meant we were separated by a window and had to talk over the phone.

The latency (which I never really notice when I'm not also looking at the person talking) made it significantly harder to have a fluid conversation than it should have been.

Made me wonder if something more old fashioned like a walkie-talkie might have been better.

This is a feature that is missing from Google Home. You can broadcast (with varying degrees of success) to other Google Homes, but nothing like an intercom. Seems nuts to me that with all their engineers they haven't implemented such a simple but powerful feature.

Nice, I've been looking to build something based around some ESP32 boards. But I can't seem to find a good echo cancellation algorithm. I guess the simple solution is to have a push to talk button on each end, but it would be nice to be able to do full duplex.

You might want to start here: https://github.com/pulseaudio/pulseaudio/tree/master/src/mod...

It would be very interesting to port that code. Another option, obviously, is to use a Raspberry Pi instead with pulseaudio and module-echo-cancel enabled.

I'll take a look - really useful - thanks!

do you think it has enough computer power to handle the audio signal?

Definitely! It's a dual core 240MHz processor. I've been running a bunch of tensorflow code on it for wake word detection.

I love this. I'm curious what the buttons do though. What's the purpose of the play queue? Are you able to see when a new message comes in?

The white buttons are a play queue of the last 4 messages I sent. When a new message arrives the corresponding button blinks.

Super cool. I'm a huge fan of very simple interfaces like that.

Very wholesome. Makes me realize it'd be useful to make an intercom system for my home.

We have a 1980s style intercom that a prior owner installed. It’s an eyesore and not even that functional. I also installed whole-house audio in 2009.

Both have been entirely superseded by a bunch of Amazon Echo/related devices, which work quite well for that purpose and background music (some rooms I was able to interface with the whole house audio, but overall I wish I had that money and time back).

As we do painting around the house, I remove the intercom panels and patch over the plaster.

I've long desired the functionality that the Echo & Echo Show provide when it comes to audio playback and intercom/video chat functionality. Unfortunately, I'm too suspicious of Amazon (and Google, for that matter) using me and my data for their own purposes. I hope to find an off-the-shelf solution some day.

> Unfortunately, I'm too suspicious of Amazon (and Google, for that matter)

For Christmas, my mom decided to get us both a Google Home and a Facebook Portal (with Alexa built in).

We already have an Echo Dot that lives on our fridge that my wife's parents gave us.

Anyway, I thought it was a bit interesting that out of the "big three" evil data stealing tech monopolies, the Google Home was the only one that made me uneasy. I suppose it's a carry over from the whole Firefox / Chrome rivalry.

I don't really care for the Echo Dot we already have, but it is admittedly quite useful for "Hey Alexa, play Christmas music" or "Hey Alexa, set a timer for 10 minutes."

Also I have been legitimately impressed by the video quality and performance of the Facebook Portal because any time I've tried to use their video chat from my computer it's had roughly a 30 second lag and been completely unusable. The Portal is both a crisp picture and no noticeable lag.

I guess the thing I should wonder most about that is why video chat from a traditional computer is so terrible. The only thing I've ever had work decently for video chat with family has been Skype.

I bought a home last year. It had been pretty well maintained, but even so it had layers of forgotten technology I had to remove. Doorbell chimes that no longer worked. The panel to a long-disconnected alarm system. Phone jacks that hadn’t been used in a decade, at least. Layers of unrelated coax runs from various satellite and cable companies.

It’s remarkable how much of a difference you can make just by skimming off the layers of antiquated crud in a room.

It’s kind of wild to me how often these things are left in place even as they’re retired.

I wish it was more common to have conduit runs for cables rather than just having them strung randomly through walls and crawl spaces. That would make upgrading from one technology to the next much easier.

We wired my parent's place during construction in 1999. A mix of mostly plastic conduit with wires fished inside and a couple of runs that were not in conduit.

Out of 56 total drop locations (many with multiple cables), we've seen the need to fish new wires down the conduits exactly 0 times in 21 years. That makes for a tough RoI calculation, especially if we'd been paying for all the labor to do the conduit installs.

Makes me realize it'd be useful to make an intercom system for my home.

Whole-home intercom systems were fairly common through the 1970's. I'm not sure why they went out of fashion.

If you're not a tinkerer, and you're in the Apple ecosystem, you can get a HomePod Mini and it will do the coordination so that all of your iOS devices can become one big intercom system, even if you're not at home. Kinda like Nextel used to do.

I had them in several houses over the years and don't think it was superseding technology that was the problem.

Intercoms were:

- kind of ugly and bulky

- fixed in place - you needed to walk over to the panel and push a button to use; but now you're already by the door (where the panels were installed) and can probably just yell faster/easier

- the person you're reaching might have volume turned down, so you resort to yelling anyway

- you might be on the phone or taking a nap and would have to turn down to volume to avoid interruption

- poor speaker/sound quality, so horrible for music playback

- poor build quality and buttons/dials would regularly fail after 5 years or faster if used

- finicky to setup with tons of manual tweaking required to get volume levels where desired

- expensive to repair & proprietary

- expensive to install

I think the answer is simply mobile phones obviated those sorts of intercom systems. Either I can yell to the person, or I can just call/facetime them.

However Apple recently introduced an Intercom / Announcement system to their homepods, so we'll try that at some point. I feel like it won't be more than a novelty unless someone knows that I'm in e.g. the garage.

I had completely forgotten that we actually had one back when I was living with my parents, because the cordless phones we had allowed you to call out and take calls, but also call any other cordless phone attached to the same base station.

We didn't think much of it at first, but it was actually super useful because going upstairs was relatively inconvenient and shouting didn't work if we were wearing headphones.

Today I guess we would just whatsapp each other.

Echo devices work for this as well, and can be accessed via any other Echo or through the Alexa app.

Presumably much cheaper than HomePod Mini too; I’ve seen the Echo Flex for as low as $10.

> I'm not sure why they went out of fashion.

Good question. Maybe smaller families and fewer multi-family/multi-generation households?

I lived in a ~3k sq ft 5 bedroom 2 story house with a total of 6 to 7 inter generational family members for a few years and it had an intercom in all the rooms. It was cool when we moved in, but after a few days no one ever used it.

Yelling was easier than going all the way to the intercom button, but even then it’s not often that you need to communicate with everyone that would justify installing an intercom system.

I would almost prefer to make my walls selectively “invisible” to sound. It would require the ability to quiet/mute as desired, but it could also be nice to just talk toward to my kid’s room, my wife’s office, etc. and be heard.

If you have multiple Echo devices you can do “alexa announce _____”

my parents had an intercom system in the house when I was a kid. they regretted it as soon as my siblings and I figured out how to operate the phones!

The Apple Watch has a walkie talkie mode which works for person to person communication.

Wonderful project. Thanks for the write up!

I like that you were able to assemble it together.

yeah, that was the best part. The gift also came with her own first set of (non toy) screwdrivers so she was pretty excited about building it.

Back in my day, we used a string and a can.


This is adorable - I love the name.

Cool! I thought you could build something even more engaging with this https://dasha.ai/en-us/developers.

Site is down sadly

I wasn't expecting so much traffic, it's up again now

You guys didn't have phones?

or you could, you know, just hug your daughter?

The only reasonable explanation I can think of why this is even necessary is that the parents are divorced and he doesn't have custody of her.

I built a web based intercom to stay connected with my parents: https://pagernation.com/


This is great! And you just gave me an idea to try and implement/code up a more basic version into a matrix room. Basically, record a voice message and drop it into a person's matrix room. (I've been on matrix since the beginning, but am moving my family over to matrix now fully as our family comms platform.) Thanks, and kudos on this!

What is matrix? This was my first try at web audio, so ya its good fun to try! If you need anything let me know!


It's a bit like XMPP.

Where were you when this discussion was happening: https://news.ycombinator.com/item?id=25526242 :)

Thanks for building this! (edit: You're a Liverpool fan? I take back what I said... :)

Damn it! This is what happens when you take a proper vacation :D :/ Oh well!

Yes I am! But we are struggling right now so feel pity for me!

this is great

Thanks! Still very beta though

Back to the analog past...

The page isn't loading.

EVERY TIME somebody attempts this yet again; 2 oldskool phones and a 9v battery! thats it, thats the whole thing!

So I never even saw the page this post is about, but somehow I can just feel that it somehow involves an overkill of brand-new digital electronics.

Like; is there a raspberryPI involved? cause I bet theres a RaspberryPI involved.

2 oldskool phones and 1 9v battery. AKA "telecom".

That's a nasty comment, it might work for you, but its not for everyone.

I for one, have created one using Mumble on raspberry, and works even better that OP's solution. I have it running on my computer, and I can mute/unmute with a mouse click. Works for me.

No, i'ts not a nasty comment, but you've interpreted it that way since you've made the same folly. I get that, that's human nature.

Yes, a RaspberryPI is a "Computer" or "Universal Machine". So literally every ACTUAL SMARTPHONE (regardless of price or ability) is a "Better Solution" than this.

a RaspberryPI for this purpose is such a waste!

"But Think Of The Children!" you cry!?

So now we're teaching the kids that the way to build a house is to buy a skyscraper and burn down the top floors? Seems like this has been goin on since the "S.T.E.M." fad and its pretty easy to see the effects if you stand back far enough.

you can run a RaspberryPI off a 9v battery too, just not for very long.

I have an intercom setup built out of old Cisco 7975 phones and a Wazo installation (a wrapper around Asterix basically) - it works decently well and the phones are durable. PoE switches (also super cheap on eBay) give me that early 2000s ease of setup.

No no no, needs more IOT Blockchain for virtual telepresence AI with chatbots that recognize family roles:

Kid: Can I have chocolate chocolate cake for breakfast?

Chatbot: ..."So I give the child a glass of grapefruit juice and chocolate cake --- nutrition. Eggs, milk, and wheat in the chocolate cake"


Sorry, this might be a dumb question but what do you mean by "oldskool" phone?

Purely analog hard-wired landline.

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