Chameth.com - posts like just-a-nod, reverse-engineering-arctis-pro-wireless-headset but not debugging-beyond-the-debugger, migrating-from-github-to-forgejo, why-you-should-be-using-https

Monthly Meanderings: February 2026

2026-03-01T00:00:00Z

It doesn’t feel like a whole month has gone past since I wrote the last instalment of Monthly Meanderings, even allowing for how short a month February is. For more context on this series, you can check out the introduction to the first edition.

Website updates

I only wrote one new blog post this month: Just a nod, which is about the “nod” button I added to the bottom of most pages. I did a lot of other little bits and pieces, though:

My blog posts are now automatically posted to a dedicated Bluesky account, and posts now include syndication links at the bottom.
The site now tracks how long each request takes to generate along with how many SQL queries were used. You can see the details for the current request by hovering/tapping over the pi symbol at the bottom right of a page. To understand why it’s a pi symbol, you should watch The Net!
Speaking of films, I redid the star rating rendering so instead of unicode stars it uses some hand-drawn pixel art stickers. They’re somewhat randomised, so they don’t look repetitive. This is what it now looks like: .
I spent some time tweaking various styles and layouts so everything works nicely on smaller screens. I try to make sure these things work when I make them, but it’s easy to miss a particular interaction, or make an innocent-seeming change that breaks tiny screens.
I added a new page that shows stats about my walks, based on my Apple Health data. I had a private view of this for a while, but decided there’s no reason it couldn’t be more public.
The films page has gained a search box, to directly find my review of a particular film. I used CSS anchor positioning for the results panel. Modern CSS is fun!
I fixed the 3D prints page being utterly broken in numerous ways. It showed up on my shiny new “how many SQL queries does each page do?” dashboard, as it was doing multiple queries for each individual print instead of just getting all the data in one go. Then I noticed a badly written redirect rule had broken all the images and download links. Whoops!
I did a lot of under-the-hood cleaning, most of which won’t be visible. Besides just making me happy, this means the contact form and nod buttons now work with Javascript disabled.
Finally, I added a page that shows my board game plays. The data comes from exports from bgstats. I have a bunch of ideas for other things to do with that data, but haven’t got around to it yet.

Phew. After writing all that out it feels like a really long month, not a short one!

Other projects

Not much going on with my other projects. The only big thing was goplum, my self-hosted monitoring/alerting tool, getting a 1.0 release. It adds a reminder feature so you can get alerted repeatedly if a service is down. It also reworks how plugins work so they’re compile-time instead of trying to be clever and dynamic, as that never really gave any benefits.

I’m still continuing my migration of projects to a private Forgejo instance. All of my personal repos are now sourced there, and mirrored out to GitHub, except one: my Dockerfiles. I’m not sure how I want to approach that yet, as the action that does the updating is pretty involved. I also have some repositories split off into their own GitHub organisations which I haven’t got around to mirroring yet.

Entertainment

Unlike the past few months, I didn’t touch many video games in February. The ones I’d been dabbling with didn’t really hook me enough to make me keep going back. I made up for it with lots of other media forms though. First up, a whole bunch of films:

I won’t write too much about them here — you can click through to read my reviews if you want — other than to call out the three excellent horror films I hadn’t seen before: Black Swan, The Cabin in the Woods, and Get Out. Not so long ago I would’ve said that I didn’t enjoy horror films, now they’re some my favourites.

I don’t have any TV show tracking on my website (yet?), as I haven’t really watched much recently. This month I started watching The Pitt though, and it rapidly become one of my favourite shows. By “started watching” I mean “watched every aired episode of both season 1 and season 2”. I highly recommend it. The only problem is that it’s hard to find anything to watch afterwards, as nothing else can quite measure up.

I’ve also been binging a book series: Beneath the Dragoneye Moons. It’s a LitRPG series: basically a fantasy setting that borrows systems from an RPG, like classes and levelling. Something about the genre really works for me, and Beneath the Dragoneye Moons is one of the more interesting series I’ve come across in the genre. I’ve been going through the series at the rate of about a book a day.

Finally, board games! Nothing particularly notable, but now I can embed a pretty display of what I actually played:

6 plays
4 plays
4 plays
4 plays
2 plays
2 plays
2 plays
2 plays
2 plays
2 plays
1 play
1 play
1 play
1 play
1 play
1 play
1 play
1 play
1 play
1 play
1 play

All of these were online via Board Game Arena. I haven’t really had time for in-person games with all the TV, films and reading!

Around the web

Start all of your commands with a comma

An old post that was doing the rounds again on Hacker News. It’s an interesting idea. I recently aliased cc to launch Claude Code with some custom parameters, and it horribly backfired when I tried to compile a C program and remembered that cc was part of GCC. I haven’t transitioned all my personal commands to use a prefix yet, but I might.

Tactical tornado is the new default

An interesting post about software developers who act as “tactical tornadoes”, and how that’s basically the role that all LLMs fill. Whenever I use coding agents, I often find myself following behind them in my IDE cleaning up bits and pieces. It’s often faster than prompting them to do it. I definitely get the “cleaning up after a tornado” metaphor.

Amusingly, the agents will sometimes notice that you’re tidying up after them and ascribe it to an automated process, outputting something like “the automated linter hasn’t run yet” if you fall behind. There’s probably a deeper philosophical discussion about what it means when the agent thinks that the human is the automated part of the system…

My smart sleep mask broadcasts users’ brainwaves to an open MQTT broker

Another one for the “the ’s’ in ‘IoT’ stands for security” books. I find it hard to actually comprehend how these things get to market. Does nobody actually think about it, or do they know full well how bad it is and just launch it anyway?

The IndieWeb and Small web

Ask three people to define ‘IndieWeb’ and ‘Small web’ and you’ll get about 20 different answers. This post by Christiano almost exactly nails my own views on the terms, and explains them well. I think most personal sites (my own included) straddle both terms to some extent, but having the labels is useful in discussions.

Just a nod

2026-02-11T00:00:00Z

Last month I added a new feature to the bottom of almost all pages on this site: a “nod” button. It’s a bit like the upvote buttons you see on bear blog posts, or the ubiquitous like button you get on social media, with one key difference: it doesn’t track or count anything. Before I get into the whys and hows, this is what it currently looks like:

The nod button in all its glory. If you want a clickable version you’ll need to scroll a bit more.

So why bother? I like hearing from people who have looked at my website. I have a contact form that’s also embedded at the bottom of all my blog posts; it’s always a delight when people reach out. Actually writing a message is a pretty high bar that most visitors won’t clear, though. A like/upvote/whatever-you-want-to-call-it is a much less demanding interaction.

And why no counting? I’d been thinking about some kind of upvote button for a while, and counting was always the thing that put me off. Having a number attached to a post like that feels like I’d end up invoking Goodhart’s law and start aiming for a certain number of upvotes or likes or whatever. I don’t want to be anxiously watching numbers, or feel pressured to make a post “good enough” (I already self-filter too much…).

As for not tracking people, that feels like table stakes to me: I’m an individual concerned about privacy, not a giant mega-corporation who wants to slurp up all the data to serve ads or engagement bait feeds. I don’t really need to know someone’s identity to receive a message from them. In the olden days of the internet, you just knew everyone by screen names which could change on a whim and didn’t reveal anything about the real you. On the internet, nobody knows you’re a dog, as Peter Steiner said.

All these constraints felt insurmountable for a while. I considered just making a button that sent a contact form submission with a pre-filled message, but those end up in my e-mail inbox. I don’t really want to have to process them, especially if there’s a big traffic spike like when Hacker News notices one of my posts. I could store the button presses in a database, but then how would I actually know they happened, especially if I didn’t want to watch a number go up?

An Amazon Dash button

So I did what I usually do with these types of problems: ignored it for a bit. The idea rattles around at the back of my head, and sometimes I’ll come up with an answer. I’ve seen this called diffuse thinking. Eventually the idea bounced to the forefront of my head while I was looking at my IRC client, and the solution suddenly clicked. If you’ve not heard of it, IRC is a chat protocol that’s almost as old as I am. Daniel Stenberg has compiled a nice history of IRC that I won’t repeat here. I use IRC to stay in touch with friends, hang around the channels for some open source projects, and I also run a private server with just me and some notification bots.

The notifications I have on IRC are all “transient”: they’re handy to see in the moment, but it doesn’t matter if I miss them. I have some high-volume news feeds, log messages from some self-hosted services, details about git commits, and so on. Basically just background noise of things that are happening that don’t need action. Perfect for the kind of interaction I want!

Now that I’d finally figured out that the transient-notification-shape goes in the transient-notification-hole, I just needed to actually implement it. As part of that private IRC setup I already have a bot that accepts messages over HTTP and sends them to a channel, so the backend was pretty simple. For the frontend I was imagining something like the ill-fated Amazon Dash buttons. My first attempt was… underwhelming:

Flat UIs are in right now, right?… Right?

I guess I shouldn’t give up the day job to become a graphic designer. Fortunately, I came across this codepen from Thierry Michel with some very fun skeuomorphic arcade buttons. I spent some time and LLM tokens on converting the SCSS to CSS, changing the colour, and making a few other tweaks. I really love how this looks and feels.

This is what it looks like in my IRC client when someone nods (and when containers get pushed to the GitHub Container Registry for my projects…):

Receiving some nods on IRC via a bot

When I added the button I wasn’t sure if I’d keep it, but I’ve very much enjoyed seeing the “nods” come in every now and then. I’ve been surprised by how many come in for the various snippets and other non-blog pages on the site. It’s a nice reminder that people are out there browsing the site, without all the baggage of monitoring analytics or tracking likes.

Monthly Meanderings: January 2026

2026-02-01T00:00:00Z

Welcome to the second edition of my monthly meanderings. For a bit of context, you can check out the introduction to the first edition.

Website updates

It’s been a pretty busy month for chameth.com. Three blog posts: The Meaning of Life — an entry into the IndieWeb carnival where I mostly review a book on Stoicism — Surge Protectors: Marketing vs Reality which is a dump of a research rabbit hole I fell into, and An Interesting Tailscale + Docker Gotcha which documents a fun problem I encountered.

I’ve also made a new films section, which is basically my Letterboxd data but free range instead of cooped up in a silo. I imported my 200-odd reviews, and for the last few I wrote the review on my site and then copied it over to Letterboxd. That’s what the IndieWeb folks call POSSE: publish on your own site, syndicate elsewhere. I like the idea that my website is the canonical source of truth for all the public things I generate. I want to expand this to some other areas in the future: music, video games, board games, etc.

I made most of the film components into “shortcodes”, so I can drop them into arbitrary pages or posts, like so:

Watched films ranked

Every film I’ve watched since I started logging, ranked.

Obviously super subjective, and subject to change often and arbitrarily.

264 films

Finally, I added a new widget to the bottom of most pages: a “nod” button. It’s effectively a “like” or “kudos” button but deliberately does not track how many times it’s been pressed, has no social network connotations, and won’t flood my inbox or hit rate limits if it gets spammed. If you click the button, it simply sends a message to a private IRC channel that says “Someone nodded at $URL”. I’ll probably write a bit more about it in a blog post in the future.

Other projects

I only have one small non-chameth.com update: a new project called pigeonhole which provides a really basic web service that lets you leave messages in a named cubby, and retrieve them at a later date. I’m using it to automate adding things to my Obsidian notes from my Apple Watch. There’s lots of reasons why that isn’t as simple as it sounds. I went through a bunch of iterations to try and make it work before just writing code to fix it.

I wanted to do this because I’m trying to replace Todoist with just having tasks in Obsidian. I already used Obsidian for longer form notes, but I’ve now also started using it for drafting blog posts (I’m typing this in Obsidian right now!), and trying to keep more useful day-to-day notes. I’ll probably write a blog post with more details once I’ve figured everything out.

Finally, I’ve been moving a bunch of projects to a private Forgejo instance, with the ultimate goal of having all of my projects live there. I’m going to mirror the contents out to GitHub and maybe other places, but Forgejo will be the single source of truth, and where all the workflows/dependency wrangling/etc happens. I’ve got Renovate configured to do dependency bumps, and I’m very much liking the whole setup so far. I’m saying it a lot but again: I’ll blog about it in more detail when it’s a bit further along.

Entertainment

I mentioned last month that I was playing Hogwarts: Legacy. I finished that off, and have been struggling to find something to scratch the same itch. I’ve tried a whole bunch of open world games, and basically none of them work for me. They have cumbersome control schemes (yay console ports), really awkward or sluggish movement, and so on. I think I’m just too fussy, but if I’m going to sink dozens of hours into a game it shouldn’t feel annoying or like a chore!

I did play through Thank Goodness You’re Here, which is delightfully funny but sadly only took 3.6 hours to finish with 100% of the achievements. Still highly recommend picking it up, especially when it’s on sale for under ‘10 bob’. I’ve also started playing through Control, and I’m enjoying the ambience. There’s an insanely sharp difficulty spike for the first boss, though, which nearly made me put it down.

In other entertainment, I’ve been playing a load of turn-based games on Board Game Arena , and I’ve watched a bunch of films after barely watching any last month. Here’s another of those shortcodes to show them off:

Around the web

Remotely unlocking an encrypted hard disk

A fun post documenting using Tailscale in a very weird way to solve a relatable problem. Very much my cup of tea.

I charged $18,000 for a static HTML page

This one’s actually from 2019, but it’s the first time I’ve come across it, and it’s a fun story. As a contractor, deciding what to bill for and what not to can be a bit messy. Downtime between meetings? The ten minutes in the shower you spent thinking through a bug? It’s a lot more clear cut if the client wants you to sit in an office, twiddling your thumbs, though.

Oxide RFD: Using LLMs at Oxide

A wonderfully well thought out piece about using LLMs in a respectful, sensible manner. I’d been thinking about writing something similar, but it wouldn’t have been anywhere near as well crafted as this. While I basically agree with it all, the part about LLM-generated text really resonates:

LLM-generated prose undermines a social contract of sorts: absent LLMs, it is presumed that of the reader and the writer, it is the writer that has undertaken the greater intellectual exertion.

Your app subscription is now my weekend project

Roberto points out that monthly SaaS subscriptions start looking even less appealing when you can just prompt an alternative into existence. I talked a bit about using LLMs for one-person software before, and it becomes even more appealing when the alternative is paying monthly for a service that keeps shoe-horning in features you don’t want, making you agree to share data with 329 “trusted partners”, and/or repeatedly ratcheting up the price.

Ekul’s Internet Space

I love the aesthetics of this personal site, and the data tracking that goes along with it. I’m also slightly aghast at the amount of Monster consumed! Makes me want to track more things and expose them on my own site.

Reverse engineering an Arctis Pro Wireless Headset

2021-06-12T00:00:00Z

The Arctis Pro Wireless Headset.

For the last year and a bit, I’ve been using a SteelSeries Arctis Pro Wireless Headset for gaming and talking to friends. It’s a fine headset, but because there’s an always-on receiver there’s no way to detect if the headset is turned on or not from the desktop.

Whenever I start using the headset, I set my desktop’s sound to go to the headset, and then when I stop using the headset I set it to go back to speakers. It doesn’t take more than a second, but some days I might put the headset on a dozen times as I’m on calls, or if it’s noisy outside, etc. That means it’s probably worth at least a few hours of my time trying to automate it.

At first, I hoped I’d be able to tell from the state of the USB device whether there was a headset connected but nothing at all changed when flipping it on and off. Then I went hunting for existing open source tools that might work with it and found that while people have reverse engineered many of the older Arctis headsets, no one has done the same for the Pro Wireless. I finished off with a search to see if anyone had documented the wire protocol even if there was no nice open source software to go with it; I came up short there, too. Looks like I’d have to do it myself.

Capturing data with WireShark

The headset exposes a Human Interface Device (HID), and the wire protocols for earlier versions of the Arctis series looked to be very simple messages passed over the HID connection. It should therefore be fairly easy to use WireShark to capture the data being sent and received by the official SteelSeries application¹.

After setting up WireShark and making it record only the headset’s HID connection, it quickly became apparent that the software was sending three different requests each second, over and over again:

Wireshark, showing a packet capture of a SET_REPORT request from the host to the headset

The packets we’re interested in are the SET_REPORT Request frames sent from the host to the device. Wireshark understands the HID protocol, so it nicely shows us the raw HID data; in the screenshot this is 0x40AA (ignoring the trailing zero bytes). The other requests sent immediately after have 0x41AA and 0x42AA payloads — clearly the first byte is indicating which piece of data is being requested.

The responses to these requests come back in an URB_INTERRUPT in frame:

Wireshark, showing a packet capture of the headset’s response to the earlier request

So the answer to our first request appears to be 0x04. The second response is 0x0402 and the third is 0x04 again. The first thing I tried doing was popping the spare battery out of the charger. The response to the 0x42AA request changed from 0x04 to 0x00 - that’s certainly clear enough! After a bit of waiting around, the battery in my headset dropped from full on the display to three bars, and at that point the 0x40AA response dropped from 0x04 to 0x03. The display on the receiver shows battery state as four bars, and it appears the wire protocol directly corresponds to that particular representation.

That left the 0x41AA request as an unknown. I tried everything I could think of, but it stubbornly kept returning 0x0402. I enlisted a friend who has the same headset to run some hacky Go code and report his values, and he also got a 0x0402 response. As I explained that I couldn’t figure out what these values are, he reported back that turning his headset off made the response change to 0x0202. In all my testing, I’d forgotten to try turning the headset off! That’s the one thing I was actually trying to detect, as well. Thanks, Simon, for helping me get past that bit of stupidity!

I still don’t know what the second byte of the response is, or whether there are other values than 0x04 for on and 0x02 for off, but I’m happy enough to label it as “device status” and move on.

Exploring other features

The software allows you to tweak a bunch of different settings:

SteelSeries Good Game software, showing the advanced headset settings

I went through each one and fiddled with all the values, recording the requests in WireShark as I did so. It turns out the protocol is very simplistic - the wire protocol directly corresponds to the UI elements in the software (or on the receiver, if you navigate through its menus). For example, the software allows you to set the “Headset auto shutoff” value in increments of 10 minutes. You might usually expect this to be converted to seconds or something similar before being passed to the device, but on the wire it’s actually sent as 0x00 for off, 0x01 for 10 minutes, up through to 0x0C for the maximum of 120 minutes.

All the dropdown options seem to function this way — if you pick the 6th option then the request payload will be an 0x06 byte. The sliders have fixed positions they snap to and function similarly: for the two brightness sliders pictured they snap to 11 positions and on the wire these range from 0x00 for off to 0x0A for the maximum.

At this point I was well past my goal of being able to detect whether the headset was on or off, and I was now just trying to see if I could figure out enough of the protocol that I could reimplement the control software on Linux if I ever wanted to. Just as I was about to close the app, something caught my eye: there are integrations with games and other software that can display information on the receiver’s OLED display!

There’s an official API for this, but it involves sending JSON to a webserver which runs as part of their app². That doesn’t feel very nice, and definitely won’t work for me on Linux, so I started a new WireShark session and took some captures while I spoke to myself on Discord.

Decoding pixels

The frames sent to the device whenever Discord showed a notification had a 1060 byte payload. The display on the receiver is 140 pixels wide³ and each pixel can only seem to be on or off, so I figured each bit in the payload corresponded to one bit of the output. I exported the data to binary in the hope that I could visually see what was going on - in theory if I line wrap the data at 140 characters it should look vaguely like the final output. Unfortunately, it did not. There was roughly the right number of high bits, but no amount of fiddling with them in a text editor could give me a coherent picture.

Instead, I wrote some code to write different values to the device. Starting with a payload of all zeroes and gradually increasing a bit at a time every second. After the first few seconds, I saw a line of pixels being drawn downwards on the left of the screen; had I just got the axes the wrong way around? After the first eight pixels lit up, though, they jumped over to the next column. The actual addressing scheme looks something like this:

Diagram of how pixels are addressed on the receiver’s OLED display

So the first 140 bytes given the pixels for the first 8 rows, the next 140 bytes fill in the 8 rows below that, and so on and so forth. Armed with this information I wrote a simple program to read an image and output it to the display:

Headset receiver displaying a custom Hello World message

At this point I was thinking about trying to get Doom rendering on the screen, but I couldn’t find anything nicely hackable that would let me grab the output and pass it on to the receiver. Instead, I decided to try a GIF decoder and before very long had a nice little animated display:

Protocol reference

All the HID messages have a single byte that determines the message type, then an 0xAA byte, then any payload required by the command. These are the ones I’ve figured out:

Byte	Command	Payload
`0x09`	Save changes	None.
`0x10`	Request firmware version(?)	None.
`0x27`	Volume limiter	`0x00` for off, `0x01` for on.
`0x2E`	Equalizer preset	ID of the equalizer preset to use.
`0x39`	Sidetone level	`0x00` for lowest to `0x09` for highest.
`0x3C`	Set headset timeout	Timeout, as a number of 10 minutes. `0x00` for off to `0x0C` for 120 mins.
`0x3E`	Mic mute LED brightness	`0x00` for lowest to `0x0A` for highest.
`0x40`	Request headset battery	None.
`0x41`	Request device status	None.
`0x42`	Request receiver battery	None.
`0x51`	Surround sound mode	`0x00` for off, `0x01` for on.
`0x62`	Auto-start Bluetooth	`0x00` for off, `0x01` for on.
`0x63`	Auto-mute game audio during calls	`0x00` for off, `0x01` for on.
`0x85`	OLED brightness	`0x00` for lowest to `0x0A` for highest.
`0x83`	Equalizer	(Not yet decoded)
`0x89`	Screensaver mode	`0x00` to dim, `0x01` for off, `0x02` for screensaver.
`0xD2`	Render image	Pixel array as described above.

Some of these I’ve not dug too much into because they didn’t seem very interesting. If you have an Arctis Pro Wireless and figure anything more out, let me know, and I’ll update the list.

If you just want to check device state like I originally did, I’ve contributed support for this headset to the excellent HeadsetControl project. It should be in the next release.

Unfortunately (as you’d expect) their application only runs on Windows, so this process involved an annoying amount of rebooting to Windows, fleeing back to Linux, and then realising I hadn’t actually recorded enough to figure it out and repeating. ↩︎
You can also send lisp to the webserver, and it will execute it. No comment. ↩︎
I know this not because it’s mentioned in the technical specs (it’s not), but because I took a photo and counted them out one by one. ↩︎

Reverse engineering the Sense API

2016-04-10T00:00:00Z

A Sense unit and its two pillow sensors

Sense is a little device that sits by your bedside and, in conjunction with a little ‘pill’ attached to your pillow, monitors your sleeping patterns and any environmental conditions that might hamper them. Android and iOS apps show you your sleep history, and offer suggestions for improvements.

Sense was Kickstarted in August 2014, raising over 2.4 million US dollars, and shipped to backers in mid 2015. The campaign blurb included this snippet:

Building with Sense

You’ll always have access to your data via our API. Take it, play with it, graph it, do whatever you want with it. It’s yours. That’s important to us.

We enjoy tinkering with and building on-top of other products we like. Sense will let you have that experience.

We’d love to hear your thoughts on what you might want to build with Sense, and how you could directly interact with the hardware, and the data it collects.

Sounds great! But a year after shipping, there’s no sign of an API, and some of us who enjoy tinkering are getting a bit restless…

Reverse engineering to the rescue

Data from the Sense hardware is transmitted off onto the Internet somewhere, and then pulled down by the mobile apps. If we can snoop that traffic, we can probably figure out how to grab the data from the Sense.

So the first step is to capture the raw network traffic while the Sense and the app are in use. I crafted an extremely over-the-top setup that involves my phone and the Sense being on a new, separate wireless network that gateways through a Linux server that can look in on all the traffic (because you never know when a dedicated capturing network will come in handy, right?…)

Running tshark while the app and device are active showed they were making HTTPS requests an Amazon Elastic Cloud instance. That’s not really much use, as we can’t see the content of the requests. The next step is to move up the network stack and target the HTTPS traffic specifically. Step in, mitmproxy. This automates man-in-the-middle attacks on HTTPS requests. When it receives such a request, it cooks up its own certificate and sends that to the client, and then sits in between while the client and the server communicate.

The certificates generated by mitmproxy aren’t issued by a trusted source, so (well behaved) browsers and apps will throw up lots of warnings and refuse to communicate with it for the most part. This is the mechanism that stops anyone impersonating your banking website when you access it over HTTPS, so is generally a very good thing. In this case, both the Sense itself and the Android app refused to talk with the blatant attacker.

We control the Android phone, though, so can just tell it that we trust the dodgy certificate issuer. This involves grabbing the certificate generated by mitmproxy, and adding it to Android’s key store. The process is documented nicely in the mitmproxy docs and is pretty straightforward. With Android trusting our certificate authority, the Sense app starts talking through the proxy and we can look at the plain HTTP requests.

The API

Logging in to the Android app and navigating through the various screens shows that the API is actually pretty nice. It’s RESTful, and uses an OAuth bearer token for authorisation, as you can see in the mitmproxy output of the authentication and first few requests:

POST https://api.hello.is/v1/oauth2/token
    ← 200 application/json 151B 1.17s
GET https://api.hello.is/v2/account/preferences
    ← 200 application/json 124B 109ms
GET https://api.hello.is/v1/account
    ← 200 application/json 181B 388ms
GET https://api.hello.is/v2/devices
    ← 200 application/json 235B 126ms
POST https://api.hello.is/v1/app/checkin
    ← 200 application/json 106B 119ms
GET https://api.hello.is/v2/insights
    ← 200 application/json 1.4kB 157ms
POST https://api.hello.is/v1/notifications/registration
    ← 204 [no content] 364ms
GET https://api.hello.is/v2/timeline/2016-04-09
    ← 200 application/json 160B 550ms
GET https://api.hello.is/v1/questions?date=2016-04-10
    ← 200 application/json 284B 132ms
PATCH https://api.hello.is/v1/app/stats
    ← 202 [no content] 126ms
GET https://api.hello.is/v1/app/stats/unread
    ← 200 application/json 71B 171ms

Authorisation

To get a bearer token, you send a POST request to /v1/oauth2/token, supplying the username and password, and a client ID and secret. Presumably if the API is ever opened up you’ll be able to register clients and get your own ID and secret, but for now reusing the ones from the Android app works fine. [I’ve prettified and linewrapped the content to make it a bit easier to read.]

POST /v1/oauth2/token HTTP/1.1
Host: api.hello.is
Accept: */*
Content-Length: 123
Content-Type: application/x-www-form-urlencoded

grant_type=password
 &client_id=8d3c1664-05ae-47e4-bcdb-477489590aa4
 &client_secret=4f771f6f-5c10-4104-bbc6-3333f5b11bf9
 &username=USERNAME
 &password=PASSWORD

HTTP/1.1 200 OK
Cache-Control: no-cache
Content-Type: application/json
Date: Sun, 10 Apr 2016 17:25:16 GMT
transfer-encoding: chunked
Connection: keep-alive

{
  "token_type":"Bearer",
  "expires_in":31536000,
  "account_id":"1234",
  "access_token":"2.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx",
  "refresh_token":"2.yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy"
}

Sleep timeline

Getting the timeline for one night is just a straight up GET request. It gives a detailed log of events, including different ‘depths’ of sleep (I’ve cut out a whole bunch here for simplicity). It also shows metrics relating to the entire night, and their condition (‘warning’ or ‘ideal’).

GET /v2/timeline/2016-04-08 HTTP/1.1
Host: api.hello.is
Accept: */*
Authorization: Bearer 2.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

HTTP/1.1 200 OK
Cache-Control: no-cache
Content-Type: application/json
Date: Sun, 10 Apr 2016 17:29:00 GMT
transfer-encoding: chunked
Connection: keep-alive

{
  "score":76,
  "score_condition":"WARNING",
  "message":"You were asleep for **8.2 hours**, and sleeping soundly for 3.2 hours.",
  "date":"2016-04-08",
  "events":[
    {
      "timestamp":1460168700000,
      "timezone_offset":3600000,
      "duration_millis":60000,
      "message":"You went to bed.",
      "sleep_depth":0,
      "sleep_state":"AWAKE",
      "event_type":"GOT_IN_BED",
      "valid_actions":["ADJUST_TIME","VERIFY","INCORRECT"]
    },{
      "timestamp":1460169600000,
      "timezone_offset":3600000,
      "duration_millis":60000,
      "message":"You fell asleep.",
      "sleep_depth":100,
      "sleep_state":"SOUND",
      "event_type":"FELL_ASLEEP",
      "valid_actions":["ADJUST_TIME","VERIFY","INCORRECT"]
    },{
      "timestamp":1460177040000,
      "timezone_offset":3600000,
      "duration_millis":60000,
      "message":"You were moving around quite a bit.",
      "sleep_depth":2,
      "sleep_state":"AWAKE",
      "event_type":"GENERIC_MOTION",
      "valid_actions":["VERIFY","INCORRECT"]
    },{
      "timestamp":1460199000000,
      "timezone_offset":3600000,
      "duration_millis":60000,
      "message":"Good morning.",
      "sleep_depth":0,
      "sleep_state":"AWAKE",
      "event_type":"WOKE_UP",
      "valid_actions":["ADJUST_TIME","VERIFY","INCORRECT"]
    }
  ],
  "metrics":[
    { "name":"total_sleep", "value":490, "unit":"MINUTES", "condition":"IDEAL" },
    { "name":"sound_sleep", "value":190, "unit":"MINUTES", "condition":"IDEAL" },
    { "name":"time_to_sleep", "value":15, "unit":"MINUTES", "condition":"IDEAL" },
    { "name":"times_awake", "value":2, "unit":"QUANTITY", "condition":"IDEAL" },
    { "name":"fell_asleep", "value":1460169600000, "unit":"TIMESTAMP", "condition":"IDEAL" },
    { "name":"woke_up", "value":1460199000000, "unit":"TIMESTAMP", "condition":"IDEAL" },
    { "name":"temperature", "value":null, "unit":"CONDITION", "condition":"IDEAL" },
    { "name":"humidity", "value":null, "unit":"CONDITION", "condition":"IDEAL" },
    { "name":"particulates", "value":null, "unit":"CONDITION", "condition":"WARNING" },
    { "name":"light", "value":null, "unit":"CONDITION", "condition":"IDEAL" },
    { "name":"sound", "value":null, "unit":"CONDITION", "condition":"IDEAL"}
  ]
}

Other interesting resources

Pretty much everything displayed in the app is available as a REST resource. They clearly put some thought into API design, which makes it even more of a shame that they haven’t made it public yet. Some of the other interesting resources are:

/v1/alarms: the alarms set on the Sense.
/v1/room/current?temp_unit=c: gives the latest environmental readouts from the Sense.
/v1/room/all_sensors/hours?quantity=2&from_utc=<timestamp>: sensor history.
/v2/devices: the paired devices, including battery status of pills.
/v2/insights: JSON representation of the cards displayed on the main screen (recommendations, analysis, etc).
/v2/trends/LAST_WEEK (or MONTH or 3_MONTHS): gives graph data for sleep scores, duration and depths.

Now the API is figured out, all that’s left is to build something that uses it…