Locating the source of a mysterious beep (simonwillison.net)

Hahaha amazing. Also cool to hear stories about headphones used as mics, I didn't think it would be sensitive enough for that.

I have almost the opposite story.

Many many many years ago, I was a wee IT manager. Sort of a weird company, I was too young to be much more than smart kid who can install / fix anything.

Anyways, worked a few years there, made some friends, had one CAD engineer who was an utter jerk. In hindsight, probably a bully, but at the time just a really irritating person.

So that was my first foray into small electronics… worked up a small breadboard with a 555, some source of randomness I don’t remember now, a piezo speaker, and a 9v battery. It would emit a short beep at random intervals between roughly 60 and 240 minutes.

Stashed it above the ceiling tiles in his office on my last day at the company.

Could you elaborate on how you converted the phase shift into a precise direction? Just a linear mapping? Or did you "hone in" by adjusting the stick until the phase shift disappeared, then proceed in that direction?

omg, I suppose the "old fashioned" way of just finding the period then anticipating it in different spots wasn't enough this time? :)

> above the ceiling tiles

So I may in the future be the villain in a story like this if I am forgetful when I sell my apartment.

My upstairs neighbor is a moron who has flooded their apartment at least twice, so I have stashed moisture sensors into the access panels in multiple rooms as a sort of early warning system.

> My wife still tells this story to all her friends as one of my biggest life achievements. Everything I shipped, the companies I founded -- pales in comparison to finding a dead smoke alarm

Do you not feel this way about it yourself? I know I would.

I brought the carbon monoxide detector downstairs to show my wife after finding it with Claude and she said "you look like a cat that's proudly showing me the mouse that it caught".

Pff that sound is horrible, and sorta hard to locate (because of the pitch?). Anyway. None of my neighbours seem to care and in summer I used to hear an orchestra of beeps every 5 seconds. It was maddening, I was contemplating of buying 1000 batteries, print a manual and shoving it in peoples mailboxes, although somehow I think it wouldnt have made a difference. I moved out eventually (not because of the beeps)

This is very humanizing. I like that.

Nicely done!

> Claude doesn’t have native audio input (yet), but it can run JavaScript and Python code that can analyze audio captured by a microphone.

LLMs can also do that with non-mic audio, btw. I had GLM (or was it qwen?) answer the question of "Why does the spotify version of the Metal Gear Rising" soundtrack sound so bad" - to great results.

Compared with the CD rips on archive.org, the noise floor was 27dB (!!!) higher, and, the whole thing was 10dB more compressed.

I cannot vouch for these specific numbers, but subtracting the good version from the bad one gave me a horrible delta wav file with lots to listen to, so there was definitely a _lot_ of difference.

It got the job done is what I want to say.

> I didn't mention this in the article, but this isn't the first time my family has been driven almost spare by a mysterious, hard-to-track beep.

https://xkcd.com/3100/

Next step isto make an iphone app and robotic arm that throws it and catches it and uses the spinning motion of the phone to triangulate.

Then its solved.

The fun part about apartment living is the weird noise can be coming from a neighboring apartment you do not have access to or control to fix.

> Move half the boxes to another room.

Alternatively, no.

Or you could use a very heavy blanked to just cover some boxes to supress the sound enough to simulate moving boxes.

It's O(logn) but you haven't accounted for how heavy each item in the array of n is.

  - the boxes are stacked
  - the heavy boxes are at the bottom of a stack, and you can't stack a heavy box on top of a light one
  - boxes aren't the same size
  - some boxes are open, so must be put on top
  - storage space and height are limited

Yes, but that's also O(log n) physical effort. This one's O(1) sitting on your butt.

(Out of curiosity: I think "physical binary search" is more properly O(n^{1/3} log(n)), or maybe O(n^{1/2} log(n)). Since physical objects have sizes, and moving things (or moving between things) takes time proportional to distance).

That requires you to stand in the room and listen for which side. So it’s nlogn times a very long time constant

You could also solve it by getting rid of the boxes of stuff you clearly don't need (if you needed it, it wouldn't still be in a box). The best way to solve a problem is to make the problem go away.

That was my proposed solution to finding something just today; it didn’t work, but one of the bags ended up containing an old contract from General Development Company. Apparently a late family member had been buying some land down there through them, but county appraisers showed that the land never changed hands until after GDC’s bankruptcy. Not even their kid had heard about this, so it really makes me wonder what the story was behind that considering they lived in the Midwest (but did have some relatives nearby in Florida).

You are moving n/2 objects log(n) times, so its O(n.log(n))

Never ignore the constant factor.

In terms of physical effort taken it’s O(n). Move half, then a quarter, then one eighth, etc.

The number of partitions doesn’t matter either, the most straightforward case is the beeping box always being in the original room, so regardless of strategy you move n-1 boxes to narrow it down, and by symmetry it doesn’t matter which room beeps.

You just look in the last box first, duh.

I love the idea of accidentally triggering this system.

You're trying to catch a fly that's been tormenting you. You clap your hands together to catch it, but it slips out. The motors on the spotlight whir. "No no no, cancel cancel!" It's too late. Your hunt now has an audience. The spotlight is on you. Your classmates are calling out when they see the fly, cheering your swats, and groaning when you miss. Even the professor is silently praying for your victory so they might be able to regain some semblance of control over the class.

This is the problem with technology. Some people just want to use it, so it's quite hard to tell whether this is really a quality of life improvement, or if it's just exciting for some weirdo (any programmer counts as weirdo here).

I've personally had to track down a beep before and used a similar technique as you suggest: time the beeps then be in right place to perform a kind of binary search to home in on it. I found a smoke alarm in the roof space above my flat, nailed to the top of the rafters that had been there since the building was built 20 years prior. It was annoying but I'm sure it took way less time and effort than "getting AI to do it".

It's still a bit surprising the first time. Especially if you've been playing with these things for years now almost exclusively with text and perhaps checking for extra fingers now and then.

I didn't have birdnet to hand and wanted to identify something. It was hard to take a picture with my phone but easy to record. Turns out one of the models was able to identify it.

I guess the Americans might appreciate gunshot identification and localisation or someone might drive around in winter/summer recording the streets to listen for heat pumps that are on the way out so they can advertise repair services. I would like a local version for movement/presence detection based on footsteps as an alternative to having pir sensors all over the place for my hall lights.

I think it was "I've lost a server"

Edit: good ol 5273

https://bash-org-archive.com/?5273

Something about:processes in Firefox, but displays sound playing.

In fact about:processes is a good enough replacement: just sort by CPU usage descending and you'll find the source in the top 5.

Hahahaha. You should slow down when you read

"The system worked as intended. It gave me the position of the beep to within about 40cm, then I dug through that specific pile of boxes and found an ancient carbon monoxide detector that desperately wanted its batteries replaced."

Sound location is slightly different from sound identification. Is the noise constant or intermittent? Could be a clothes washer or drier, could be a sound system, could be pipes and water, could be sound transfer along a surface.

> I tried recording it with my phone, but it doesn't pick anything up.

Doesn't pick anything or doesn't pick anything that you can hear back? Might still be worth giving for processing to an LLM as some nerd is able to locate a webcam location from the recorded sound and date [1].

[1] https://www.youtube.com/shorts/4CEHH2WyRKs

The problem was actually described in the agent output that I hadn't read when requested that additional feature:

> Distances only fix the layout up to translation, rotation and mirror image. That doesn't matter for the maths, but the map I'm shown has to match the real room, so the UI needs "rotate" and "flip" controls, or a way to say "Blue is next to the door".

https://github.com/simonw/beep-locator/blob/main/problem.md#...

You can time the envelope of the ramp, though

Thanks, Vetinaris clockmaker.

Great thing for tool checkout/rental at a makerspace!

You can also build one pretty cheaply and simply with the miniDSP UMA 16: https://www.minidsp.com/products/usb-audio-interface/uma-16-...

https://www.minidsp.com/applications/usb-mic-array/acoustic-...

Oh, was gonna post a comment about this, I actually bought just last week their USBc version (Fotric Sonic 3), on eBay, for around $700. Works quite well, it has 64 mic array, I think it would be tough to replicate it to this level.

Lmk if anyone has any questions about it! It’s android-only, but I’ve gotten an agent to write a Mac version of it though haven’t tested yet.

eBay link to what I bought: https://www.ebay.com/itm/960060893216

Does it work for infrequent sounds? The sound might for example come in the middle of the night for two seconds, loud enough to wake one up, then go away. If I leave it on, can it do continuous recording and max or threshold-based capture?

It seems what happened with thermal cameras many years ago might be happening with acoustic ones now. They used to cost a lot more than that.

Yeah, I wouldn't do this for code that I was expecting anyone else to review.

This is actually the first time I've told an agent to write out a "problems.md" document - it was an experiment to see if stating the problem provided decent results, as opposed to working directly on a spec.

It did seem to work well though. I was outsourcing as much judgement as possible to the model, and the model did a good job at making decisions that got me to my required end result.

In this case, the AI could do the reasoning for me. Opus 5.5 and Fable 5.2 are really good!

> In fact (or IMO?), this "problems.md" document is entirely unnecessary. In many cases, simply describing the issue and providing the relevant context is enough for AI to come up with a working solution.

I don't mean to respond to your 'professional work' scenario, but I find it quite useful to first let it draft a PLAN.md, even when "in many cases" it would one-shot some implementation without it. I mostly prompt it with a problem statement, "write a PLAN.md", "ask me any questions in prose and numbered", "don't start implementation until my say-so". The back-and-forth questions are often pretty significant to the final result, and I can (skim) review the plan and make other adjustments.

When you ask most models to write that plan, you see an extended thinking trace similar to implementation itself, but now all the decisions are made up front. If you one-shot it an implementation, those decisions are sprinkled all over the implementation phase, while half of it has been written and some architectural choices have already been locked in. I then frequently adjust that plan to end up (IMO) with a much better implementation, or much better suited to my situation, with less shortcuts.