Box of Secrets: Discreetly modding an apartment intercom to work with Apple Home

https://www.jackhogan.me/blog/box-of-secrets/

by jackhogan11 • 4 months ago

283 114 4 months ago

greggsy3• 4 months ago

I’m actually pretty surprised how bad the intercom ecosystem is these days.

Why aren’t there more ‘semi dumb’ Ethernet or wifi products that just let you announce that dinner is ready? It doesn’t need to be a fully ruggedised commercial system like this one or a fully integrated cloud managed solution like ring.

The cheap no name wireless ones can’t handle comms between rooms, let alone across a house.

The security implications aren’t insurmountable - you could use pairing codes if there are multiple on the network.

I’ve accepted that it’s a niche market, and that the only solution is to use Asterix with a some cheapo voip phones.

fragmede2• 4 months ago

There's Butterfly and another company I can't remember and undoubtedly more, that have expensive systems for large complexes, so the niche is the small buildings that don't have a ton of money. Maybe the softwarepocalypse can help with that.

unsnap_biceps• 4 months ago

Apple's HomePod Mini and Google Home and Alexa all support intercom modes. I'd presume they typically handle the home case for the majority of folks.

arjie• 4 months ago

We have Google Home Minis in every room and the screens in bedroom and kitchen and the only thing that works reliably to message intra-room is to say "Hey Google, broadcast message" because half of the time it will tell me it can't send messages yet. If someone knows what I'm doing wrong I'd love to hear it since this would be a great feature.

To be honest, I'm honestly sick of Google Home's approach to this since the Gemini update has turned everything really slow and I'm getting close to the point where I'd rather home-roll a full system myself that works reliably instead of the crapshoot that this is. Home Assistant seems to have a functionality bridge to Google Home connected devices like my blinds or cameras so I should be able to retain the edge devices but I have half a mind to just dump the whole thing and start over.

pprotas• 4 months ago

HomePod Mini is a waste of money, unless you like screaming at your dumb robot that never understands what you want it to do

Setting timers works well though

greggsy3• 4 months ago

Tried that. Hated it.

adamesque• 4 months ago

At least on the HomePod side, intercom is at best a half-baked feature and at worst an infuriation machine. It uses a cumbersome voice trigger ("siri, tell <room>…") to begin recording audio, with no clear indication of when recording began and no way to know for sure that the audio was directed where you wanted it to go.

To respond is similarly cumbersome and soon you give up completely. I can only assume it was designed by someone whose parents were killed in an intercom-related disaster and has sworn revenge.

I bought a mini for my office with this purpose in mind, but it has been a total waste.

lnx01• 4 months ago

*Asterisk

bombcar3• 4 months ago

I had a surprisingly working intercom setup with Asterisk and some old Cisco phones set to auto-answer on speaker. But ... complicated setup and eventually it fell into disuse.

zer00eyz• 4 months ago

Everything involving audio is an annoying mess.

The first step is getting speakers in a room: there are tons of products that do this, apple, google, Sonos.

Most of them have the audio quality of a bag of instruments.

There are tons of class D amps that you can hook up to speakers: Wiim, acrylic and so on... this will run you anywhere from 100 bucks to 500 and thats before you buy the speakers. Most of these will be great for playing music and projecting your voice.

The moment you involve a TV... well things get ugly because your going to want arc for HDMI and your going to want a center channel cause with out it your likely in subtitle hell half the time. This will get expensive a Sonos sound bar is a few hundred and if you want something better well... Let's say you can get to the point of making a GPU look affordable real quick.

Now that you can play audio, how do you hear it... well your phone works and there are tons of satellites out there.

You're now going to need to run home assistant to "interrupt" what ever is playing (if something is) to play your message and then return what ever it was to its current state.

After trying out WIIM, Acrylic, some high end stereo gear I just settled on half assed audio quality and bought more Sonos gear. I kept a single WIIM unit, cheap amp, decent speakers and a sub around for when I want to really listen to music but other than that I tolerate sonos' middling quality for day to day use (and I am, by no means an audiophile).

prmoustache4• 4 months ago

Why aren’t there more ‘semi dumb’ Ethernet or wifi products that just let you announce that dinner is ready?

Because of 2 reasons

1) this is very antisocial behavior.

2) so many people have a mobile phone at arm's reach a majority of the time so there you have your intercom.

Well educated members of an household would know when dinner is ready because they would actually help make it ready for everyone. Occasionally one teenager could legitimately focus on homework but it is not actually a bad thing that someone has to move its ass and walk upstairs to knock at their door and tell them. We call that free exercise, much cheaper than a fitness subscription.

When I hear about home assistant and domotic in general, the only image that comes to me is those scenes in Wall-E where people live in a flying armchair with a holo screen in front of their face 24/7, their only interaction with a physical world being to only move their arms once in a while to grab a soda.

When I was a kid I remember a house we rented for a while came with intercom using the electrical lines. Past the initial novelty, they mostly collected dust and ended up being unplugged.

greggsy3• 4 months ago

It’s not antisocial… at all?

I’m genuinely confused why you would think that.

Well educated members of an household would know when dinner is ready because they would actually help make it ready for everyone.

This is one of the most obnoxious things I have read all year.

stavros• 4 months ago

The Home Assistant Voice will let you do whatever. I wrote a small server that accepts the audio and plays audio back, but you can also send audio whenever you want. They're very nice little devices.

jeffwilcox• 4 months ago

Was always wanting to do something like this before they swapped ours out for a SaaS+hardware butterfly mx thing.

Those Doorkings have had to get replaced at so many buildings in Seattle now that criminals figured out how easy they were to override.

bombcar3• 4 months ago

Naming the product "dorkings" was certainly a choice.

FlorinSays2• 4 months ago

I had the same problem and I've searched for ready made solutions for over an year before I found a guy that reverse-engineers and builds ready-made boards to install in my intercom for less than 30 euro.

I'm unsure if I should post the link or not as it's specific to Romania, but I love how janky the buids are: https://www.olx.ro/d/oferta/automatizare-interfon-electra-cu...

close043• 4 months ago

Some years ago I had an older analog intercom and added some intelligence for the open button, ignoring the audio part. Doing it with an ESP01 was trivial and I only needed access to my intercom box inside the apartment. The first issue I ran into was that no matter how much I optimized, the power consumption was high and made the thing semi-useless. Then I got smarter and powered it from the 24V lines coming from the intercom system. That worked great until I realized that where I live this counts as stealing electricity so I scratched that, why take the chance that the building administrator notices something and I get burned.

Eventually I got a Nuki Opener which works with all kinds of intercoms and is way less effort. Janky builds are awesome but better for the playground than as a solution you really want to be reliable for the whole family.

P.S. The code from the article should be linked more prominently [0], for anyone who wants to tinker.

[0] https://github.com/ImTheSquid/doorbell2

RealityVoid• 4 months ago

I don't understand how the Nuki Opener works. You still need to open your intercom and solder, right?

FlorinSays2• 4 months ago

Janky builds are awesome but better for the playground than as a solution you really want to be reliable for the whole family.

I have it configured with a delayed opening so that it's not obvious, it doesn't require an app, and by the time you reach the door, the guest is almost there.

When I'm done with it, I flip the switch. It's hard to have it more reliable than this for me.

I've been considering smarter iterations for myself, but I didn't find enough time to fix something that is working really well.

wzdd• 4 months ago

Fun. I did this recently with mine. There's now a discreet USB cable running down from behind it...

cryptoz• 4 months ago

Related, I'm still upset at the lies told by landlords regarding phone number privacy in buzz-in intercoms. I've been told multiple times at multiple apartment buildings, "don't worry, while the system will call your phone when someone taps your entry code, your phone number won't be revealed". And then you sign the lease, get a delivery from Instacart in your new place, and find that your 'private' number is blasted out loud, heard a whole city block away, in a loud-ass DTMF tone sequence.

BS.

anilakar2• 4 months ago

Frank's guests just need to get the Doorking 16120 default key and start letting themselves in.

Edit: undergrad shenanigans from ten years ago:

Our university student-run electronics lab had an issue: technically anyone with a student card was allowed on premises at any given time, but the department only gave us a small set of keys that we had to share with the rest of the student associations. Obviously we needed a solution.

We did some snooping and found that the request-to-exit button wire was running on a cable tray alongside all the other wiring and plumbing, as the lab was in the basement. We picked a suitably dark, inconspicuous spot and wired up a Raspberry Pi driving a transistor and in turn a relay which we then wired in parallel with that button. Users could then connect to the local lab wifi and then SSH into the device. Login shell was replaced with a script that pulsed the GPIO line for half a second and subsequently caused the door to open.

We never got caught and apparently all the evidence was destroyed when the building was renovated a few years later.

nunez• 4 months ago

Brilliant!

eastbound• 4 months ago

The upside is that this is perfectly SOC2-compliant, as long as auditors don’t find out about the Raspberry.

ThePowerOfFuet• 4 months ago

What Raspberry? I don't see any Raspberry.

ChiefTinkeer• 4 months ago

...and if your compliance provider is Delve then you don't even need to worry about that!

fennecfoxy4• 4 months ago

A whole ass pi just for that?!

nkrisc3• 4 months ago

What would you have used ten years ago?

anilakar2• 4 months ago

We had to come up with something wireless for authentication as we did not want to install anything visible like RFID readers. We also had a few Pis lying around.

sneak2• 4 months ago

Confessing to felonies, in writing, under one’s real name is wild.

Here’s hoping nobody decides to bother them about this. I’m not a lawyer but this appears to this layperson at the very least a CFAA violation by accessing the router and resetting its root password, as well as possibly criminal mischief as well as whatever stealing AC power is.

You couldn’t pay me to do a writeup like this, and I’d be wearing gloves the whole time.

Hackbraten3• 4 months ago

How is it stealing power if the power is exclusively used for restoring a service or system that the tenant is paying for?

hparadiz• 4 months ago

It's a repair from where I'm sitting. A really cheap one too.

qaadika2• 4 months ago

I felt myself starting to sweat as I read. I can't imagine doing this at my apartment complex, let alone at someone else's. Messing with building controls (old or unused as they may be) sounds like a great way to get your lease nixed and your ass out the door quicker than a lawyer can say "Yeah, I can't help you here, they're well within their rights to evict you for that."

I was hoping they'd mention something about the legality (or lack thereof), but I guess that's an exercise left to the reader who wants to try this out at their own apartment.

Hackbraten3• 4 months ago

sounds like a great way to get your lease nixed and your ass out the door quicker than a lawyer can say "Yeah, I can't help you here, they're well within their rights to evict you for that."

For repairing a broken thing? After provably trying in vain to get the landlord to fix it?

fennecfoxy4• 4 months ago

Meh. Plenty of landlords suck, if anything his only mistake was not making it available to others in the same building.

The last apartment I rented (London) I never even met my shitty landlord hiding all the way up in Scotland. Randomly one day after getting home from a long day at work, my fob wouldn't let me in at the front door. Message the landlord ("SMS only, no calls") and it turns out that he'd got another copy made in case he needed it - when he got this copy made, the security company disabled the current fob (my one).

Initially he was going to make me wait until a new fob could be sorted out. After much anger and aggression I got his fob sent down to me in the post. Was still not able to access my home for several days and had to emergency crash with some friends.

Didn't get a discount on the rent and the fucker came up with every excuse under the sun to take my security deposit upon moving out as well.

blitzar• 4 months ago

I use a Ring Intercom Audio for a similar use. Works surprisingly well, I wish someone would clone the hardware and make an open version so Jeff didn't listen in every time someone rings my doorbell or buzz himself in whenever he wants.

No native apple home - homebridge handles that.

sharklasers123• 4 months ago

I did similar in my apartment in Amsterdam but a little more low-tech. I soldered the relay on an Esp8266 directly to the unlock button on the intercom PCB in my apartment. Worked flawlessly for years

dwedge• 4 months ago

Of course it had to mention Claude and Rust haha.

That aside, I enjoyed this read and it's such a niche thing that there is almost no way they'll step on the toes of another resident wanting to do the same thing

dosinga• 4 months ago

I ended up using https://eu.switch-bot.com/products/switchbot-bot -- just have a finger robot push the button

foota• 4 months ago

Hah, I did the same exact thing and came here to say that :) I was looking at wiring diagrams and telling myself I could wire up some arduino circuits for it but gave up when when I realized I could just press the button!

edit: although mine was an ancient system from the early 90s. It was just replaced with a modern system a couple months ago. At my previous apartment I had wanted to set up a system that would allow either my then partner or I to activate the callbox and have it set for a VOIP number since we could only put one number on the box.

beardyw• 4 months ago

It's a little sad that, having realised that the simplest route for the hardware was the best, a simple route for communications wasn't explored. I suspect that cramming in a complex stack wasn't the best or quickest solution.

xmlninja• 4 months ago

Great, the esp32 will probably never be discovered. Because when the landlord decides to fix the original problem, the whole unit will probably be replaced.

robjampar• 4 months ago

I have a similar Apple HomeKit integration to my apartment door system in a much simpler way;

When you buzz the apartment from the intercom it connects to a dedicated landline phone, That landline is setup to automatically go straight to voicemail, and then the voicemail message is just a recording of the tone required to open the door.

Then I have a smart power socket that the landline phone gets its power from - which I can toggle in the home app.

So if you turn on the power socket and dial the apartment code at the entrance, it buzzes you straight in. Or turn the power socket off and it doesn't.

kelnos2• 4 months ago

That's pretty cool! If it were me, though, I'd be afraid that I'd forget to turn the socket off after using it.

I guess I'd also set it up so right after the voicemail message runs and lets someone in, it would turn the socket off.

rahimnathwani• 4 months ago

This is cool.

But it wouldn't work for OP, whose door intercom can no longer make phone calls.

jonpurdy• 4 months ago

I do something similar with voip.ms (hosted Asterisk).

The intercom calls my voip number, which can be set two ways: 1) play DTMF tone 9 to let the person in, then hang up (which is a security risk if random folks at the intercom buzzed me up trying to get in.

Or 2) plays audio "enter passcode", then:

- if the visitor enters the code that I told them, it plays DTMF 9 to let them in

- if the code is incorrect, plays "incorrect passcode" and hangs up

It also sends an email and SMS whenever someone triggers the intercom so I know about it. With passcodes, I can even set up multiple passcodes to give out to various people (like Amazon, friends) and my notification will display which code was used.

jojobas• 4 months ago

Backdooring common property with questionable technology? Sad.

matsemann2• 4 months ago

This reminds me of another annoyance I have. We have a wall mounted thermostat using batteries at the cabin. It controls how much water is let through from the central heating to the floors by sending some radio signal. I would like to be able to control this remotely, for instance to turn on heating a day before arrival. But the only way to do this is to buy a new unit connected to the pipes as well and upgrade the whole thing, which was quoted like $2k++ and need their app and their subscription. But why can't something just mimic the radio signals? That already works today! Why do I have to rebuild the whole heating setup for this? So stupid when technology locks you in without need.

I'm tempted to have a remote controlled screw driver that can twist the knob remotely or something.

kapep• 4 months ago

Take a look at SwitchBot. They have a device that can tap buttons to solve these kinds of problems. They also have a device for tilting blinds by twisting the rod, which could maybe be modified to twist a knob.

gib4442• 4 months ago

I know some cabins are quite remote but do you have a trusted neighbour who would do it for a case of beer?

My mum's neighbours buy milk and bread and turn the heating on! I don't quite trust my own neighbour to do that but it's awesome for her

matsemann2• 4 months ago

I like your approach, it's one I try to use at work as well. Not every problem is a tech problem, many things can be fixed by just talking to humans or changing the process.

In my case the cabin is actually in the town where I grew up, and used as a way to be closer to home and family without overstaying my welcome and also be a bit more free when here (heh). So I do have family that now helps with this, it was mostly in a "can I pay a little not inconvenience them". I arrived here sunday with the heat on and some easter eggs and bunnies on the table put there by my mother, so it's not all bad. :)

ffsm8• 4 months ago

There are often controllers which do indeed just mimic the signals. Doesn't work with every appliance, it depends on the way it's implement and if the manufacturer wanted to make that approach infeasible.

But there absolutely are options to record such Signals and then replicate them via home assistant - I used them before to control a ceiling fan and various infrared devices (same idea, but not a radio there instead a "blaster" - I think it was called)

I didn't set it up again after my last move though, as I couldn't mount the ceiling fan in this apartment and the Infrared devices were just my media center (tv, audio), which are hardly in use currently

bombcar3• 4 months ago

The key with all furnace/heating/cooling automations is to start at the source of heat - figure out what IT needs to do what it wants, and work from there.

They're almost always incredibly simple at the furnace/boiler - you just need to make sure that you never turn the heat on without the pump/blower or whatever is required.

My complicated Eco controller ends up with three outputs: blower on, heat on, cooling on. Three wires.

IncreasePosts2• 4 months ago

If it's actually using radio, almost certainly there is a radio receiver unit at your furnace which converts the radio commands to simple voltages on physical wires, likely to power a 24v solenoid. All you need to do is hook in a esp32 or similar to also send those voltages when it receives a command.

peralta• 4 months ago

For some European intercoms, there is Doorman [0]. Their authors reversed engineered the protocol used by Koch and built an ESP32 + Home Assistant solution that works quite nicely (including board). The "party mode" [1] was a life saver for me when doing events on the rooftop.

[0] https://doorman.azon.ai/ [1] https://doorman.azon.ai/guide/features/ring-to-open

secure• 4 months ago

I built something similar! https://michael.stapelberg.ch/posts/2021-03-13-smart-interco...

I bought the cheapest compatible BTicino intercom device (BT 344232 for 32 €) that I could find on eBay, then soldered in 4 wires and added microcontrollers to make it smart. It now connects to my Nuki Opener Smart Intercom IOT device, and to my local MQTT Pub/Sub bus (why not?).

mememememememo• 4 months ago

Tldr: he found the wire to the solenoid. Cool stuff. Do the easy thing! The rabbit hole avoidance was impressive. Like an escape room of sorts. Questionable legality notwithstanding.

bdeol222• 4 months ago

This is a good way to breathe new life into existing tech for your smart home ecosystem. My setup mainly consists of Philips Hue lights at the moment, which. I have hooked up using Openclaw, I'd love to add more smart functionality and like an intercom, thermostat and digital lock, but the current devices are stuck in the past, so cant do much at the moment.

rsafaya• 4 months ago

What are your thoughts on OC security?

bdeol222• 4 months ago

I keep mine locked down with access only to my own chat. Hopefully that keeps it from leaking my API keys to the universe.

randallsquared• 4 months ago

Part of the plan: Write firmware for an unfamiliar microcontroller. Also part of the plan: Don't spend the entire vacation...

I love the future so far.

detourdog• 4 months ago

When I was shopping for an intercom system for my 8 unit building I purposely went for the dumbest system I could find. I wanted it as a foundation and isolated from the rest of the world. I also wanted no cameras.

Here is the installation documentation I have the 4-wire system. I installed it using Cat-5 and standard 548B wiring layout. The rest of the electronic door locks uses the Identiv Liberty key fob system. This was the only system I could find that allowed self-hosting.

I wouldn't mind another layer of integration that would add smartphone access control. The way the 2 systems are currently deployed I could ignore the TekTone side and just integrate the key fobs with the smartphones. I think this might already be possible be possible as the key fob readers already react to the NFC radios on my smartphone.

https://www.tektone.com/pdf_files/manuals/IL826_PK543A_insta...

massimoto• 4 months ago

Legally and ethically extremely dubious, hooked up to the box in your apartment, I can understand it. Hooked to the shared door controller, handing out access "keys" to all your friends, not great. You seem to know this based on all your attempts to avoid discovery.

netsharc2• 4 months ago

This place is "Hacker" in name, but not in spirit...

natpalmer1776• 4 months ago

A lot of us grew up and realized that while we avoided many of the consequences of our actions, some of our peers did not. Thus the caution (and concern for other uninvolved parties)

Personally, I’m of the opinion that this kind of thing should be done by those who understand the risks and accept them regardless. It’s fun and interesting, and in the real world it will almost certainly never be an issue.

pesus• 4 months ago

There has always been ethical and unethical hacking (and shades of gray in between).

IncreasePosts2• 4 months ago

It's unethical to increase the risk profile of unaware third parties because you're a hacker.

I'd be fine installing this in my own house, but it shouldn't go in a shared space.

in fact, I've done something similar, wiring my unifi door bell to be able to unlock my matter-enabled deadbolt via an esp32 in the wall.

neilv• 4 months ago

That and more, IIUC. They've:

* Given access to more people or other ways.

* Bypassed any logging that might be used during crime investigation.

* May have increased the likelihood of the system failing.

* (more theoretical) Increased the attack surface, and invited more crimes of digital opportunity.

So they may be partly or wholly responsible for some bad things that happen.

And also may be held responsible by others, with criminal and civil liability.

[...] so if you’re in the same position as Frank, give it a try!

Don't, if you're in the same position (i.e., sneakily doing it to landlord's access control box, which is relied upon by multiple other neighbors).

But if you're in some different position -- such as it's your own property, and there's some kind of informed consent of all legitimate parties affected -- then kludging the system, by splicing a solenoid wire, might be good and appropriate.

shepherdjerred• 4 months ago

I totally agree provided Frank lives in some maximum-security apartment complex with armed guards. Otherwise I think you'd making a big deal out of nothing.

Anyone can get into a complex by following someone else in.

Or, in this case, just power the solenoid wire that is _already outside_ as the OP did.

4fterd4rk• 4 months ago

Meanwhile out here in the real world no one gives two shits and if it was ever discovered a simple "what? I have no idea what you're talking about." would provide all the cover needed.

pavel_lishin2• 4 months ago

My mom's condo building hasn't had a working buzzer in forever, so she has to go downstairs every time there's a delivery. I've been tempted to do this, but am highly discouraged by the presence of video cameras. I don't particularly want to catch a charge to save my mom a trip in the elevator.

netsharc2• 4 months ago

Wear a high-vis vest or one with the company branding? By the time they figure something out it's probably beyond the 24-hour recording retention period...

pavel_lishin2• 4 months ago

I appreciate you helping me commit a crime, but I'm going to go on record saying that I'm not going to risk it :)

Egonex• 4 months ago

This is a very interesting project. Protocol choice on constrained hardware like this is always underestimated, most people default to JSON over HTTP, but on devices with limited MTU or battery constraints the overhead adds up really fast.

We have seen similar trade-offs working on binary encoding for our alerting systems; even a few hundred bytes difference per message changes what's feasible over BLE or LoRa. What protocol the intercom uses natively and how much of the HomeKit overhead is format vs transport?

thedanbob• 4 months ago

While it is theoretically possible that the relays could fail on through some sort of physical failure, this is so unlikely that we did not design for it.

Anecdotally, I've had a relay fail on when I inadvertently pulled more amps through it than it was rated for, so it's definitely possible.

Animats• 4 months ago

The relay they're using is quite likely to fail. It's a no-brand imitation of a relay where the real one is only rated for 10^5 cycles driving an inductive load.[1] Also, they needed a DPDT relay, which they are emulating using two SPDT relays operated together. If the software ever operates only one of them, the door will remain locked regardless of what the entryphone box does. Also, no fuse or snubbing. There's a whole industry of really crappy control relays from China, especially on the solid state relay side.

A useful device to know about is the Relay In A Box line.[2] This is exactly what it says - a relay in a box, for when you need to switch power with a low-voltage control signal. UL and CE approvals, fits standard electrical conduit fittings, and will pass code inspection. Rated for 10 million cycles. Boring, but useful.

[1] https://www.alldatasheet.com/html-pdf/1132639/SONGLERELAY/SR...

[2] https://www.functionaldevices.com/category/building-automati...

alfanick• 4 months ago

This looks like a very guest-hostile intercom, I would just stare at it and read instructions, then read them again, then think why is it A and Z and not up and down... And also why I cannot just enter the number. At some point I would give up and just take out my phone and call the friend "hey, can you buzz me in? I'm in front of the door".

spankalee• 4 months ago

I did something a lot simpler than this to have some more control: I gave a Twilio number to the building manager for the door box, then had an app where I could give out codes to people. Valid codes responded with a "9" DTMF signal which opened the door, a "1" forwarded the call to my phone.

josefritzishere• 4 months ago

This is quite illegal. (More in some states than others) Just working on an access control system without a license is a crime in most states. It's actually a felony in North Carolina.

The_President• 4 months ago

Which states are these where it is illegal to perform unlicensed work on an access control system?

kelnos2• 4 months ago

Years ago I was renting a condo in a building with a bit of an older system; on the outside there were a series of buttons, each hard-wired to each of the condo units, where the units had a phone handset on the wall, with a button on the base to open the front door. Just three wires, IIRC.

I only had one key to the main door, which was annoying when I had guests who were staying a few days. It finally got annoying enough once I had a steady girlfriend who was more or less unofficially living with me. So I opened up the handset base, figured out the voltage on the wire for opening the door, and got a Raspberry Pi and a relay rated for the voltage I needed. I connected the relay's control pin to a GPIO on the Pi, and wrote a little python HTTP server that would enable the GPIO pin, and fire off a thread to turn it back off after a few seconds.

I was working at Twilio at the time, so I figured the easiest trigger would be SMS. I set up a phone number, and the backend logic for it had a list of sender phone numbers and 6-digit codes. That way I could only allow certain people's phones to trigger, and on top of that, it required a code, unique to each visitor I was allowing. It would also send a text to me every time someone used it, so I could monitor things to ensure nothing odd was happening.

I already had a small home automation system running using openHAB, with remote access set up on a VPS I rented, so it wasn't hard to hook all that together, in a way that the callback handler from Twilio could reach back into the home.

I didn't have a great way to mount it, and didn't want to mess up the wall. The Pi and relay were light enough that I ended up just hanging it from the wires connecting to from the relay to the handset base. Fortunately there was an electrical socket almost directly below the handset so I could plug in the Pi. (I forgot about it when my landlady had to come over due to a water leak; surprisingly she didn't even comment on it.)

My one worry was that the little python HTTP server would crash between closing the relay and then opening it up again after a few seconds, leaving the door persistently unlocked. But I used a default-open port on the relay, so if power went out, the relay would stay open, keeping the door locked. I also made sure that the little HTTP server would reset the GPIO to keep the relay open on startup, so if it crashed and restarted, it would ensure the door was locked. IIRC there was also something you could put in the Pi's /boot/config.txt to set GPIOs to a certain value on boot(?). And on top of that, I wrote another little python script that just sat there checking the GPIO every second, and if it remained on for more than a few seconds, it would close it. This was probably overkill, but I wanted to be as sure as possible I wouldn't be putting my neighbors into any kind of danger by perma-unlocking the front door.

Something like an ESP32 would certainly have been smaller and lower-power (maybe could have even run it off battery), but at the time I hadn't even heard of ESP32 yet (that would come a few years later, when I was bored during the pandemic and needed a project).

Box of Secrets: Discreetly modding an apartment intercom to work with Apple Home

Related Stories