Show HN: Offline SOS signaling+recovery app for disasters/wars
88 comments
·April 1, 2025eddythompson80
> It can also be improved; I know BLE is not _that_ effective under rubble.
It's a tough problem to solve because you're up against the laws of physics and the very boring (and often counterintuitive) "Antenna Theory". Bluetooth is in the UHF band, and UHF isn't good for penetrating anything let a lone concrete rubble.
To penetrate rubble effectively you really want to be in the ELF-VLF bands, (That's what submarines/mining bots/underground seismic sensors use to get signals out).
Obviously that's ridiculous. Everything from ELF to even HF is impossible to use in a "under the rubble" situation because of physics[1]. Bluetooth (UHF) might be "better than nothing" but you're losing at least 25-30 dBs (which is like 99.99% signal) in 12 inches of concrete rubble. VHF (like a handheld radio) can buy you another 5 inches.
Honestly I think sound waves travel further in such medium than RF waves.
[1]: Your "standard reference dipole" antenna needs to be 1/2 or 1/4 your wave length to resonate. At ELF-VLF range you need an antenna that's 10k-1k feet long. You can play with inductors and loops to electrically lengthen your antenna without physically lengthening it, but you're not gonna get that below 500-200 feet. The length of a submarine is an important design consideration when deciding on what type of radio signal it needs to be able to receive/transmit vs how deep it needs to be for stealth.
nizarmah
Thanks for the amazing breakdown.
That means LoRa and cellular network won't help either... That's good to know.
Yeah, sound seems like a good option. There's two points I'm struggling with though: 1. Disasters often are accompanied with a lot of noise which I'm afraid would drown or interfere with the other sound waves. 2. Mobile devices might not be able to detect the sound waves that are broadcasted.
I'll need to do more homework about those.
We'll have more flexibility with recovery for sure, so maybe that can address the shortcomings of the sound signaling...?
It still has to be cheap-ish though. Because first responders already have MUCH better tools [1].
Again, thank you so much for this comment. If you have any other suggestions or feedback, please don't hesitate to open an issue on github. Your input is awesome.
[1]: https://www.dhs.gov/archive/detecting-heartbeats-rubble-dhs-...
eddythompson80
> That means LoRa and cellular network won't help either... That's good to know.
It does. If anyone is buried under the rubble "why don't they just tweet/SMS/mesh-network they are stuck" might be the first question someone would have. A simple answer is that the nearest GSM tower is also under rubble. But that's not enough. Even if the nearest GSM tower is 100% fine (or their next LoRa mesh peer is also fine), you need to be less than 12-15 inches of concrete (in the most optimal/reflective way) to have any signal at all. At the end of the day you're up against physics. 3 questions physics mandates:
1. What is the wavelength you're transmitting?
2. How far is your receiver?
3. What is your medium?
The keyword "Antenna Theory" or "Antenna Design" is a good rabbit hole for this sort of thing. There is this funny saying among radio enthusiasts "everything is an antenna if you squint hard enough"[1].
There is also something that cooks call "The Human Element"[2] when they're trying to evaluate the appeal of some foods to people. The "Human Element" in an "under the rubble" situation is that you want something that a normal human being would have on them when the sudden situation of an earthquake happens and they find themselves under a rubble.
I don't know what that is. I live in a place that is pretty far removed from earthquakes as a major problem. Geologically speaking, we get a "major earthquake" every 500 years or so. However, that's an average and it's been 600 years for us but the max has been 3,000 years and the min has been 200 and the mean means nothing to the individual. However, a device of some sort that can emit low frequency, low bandwidth[3], long range message seems like a useful thing. I don't know if that would be the type of device every human would have "on their body" all the time. But maybe??
[1] Everything that's electrically conductive is an RF antenna. If you get buried in the right place next to a 100 feet long rebar, you could (theoretically) send a signal that anyone in 100 mile range could hear provided you had the right equipment of course.
[2] In cooking, it is this elusive thing that explains how some cultures/people love certain tastes or textures that other cultures don't. Slimy foods in Middle Eastern or Japanese/Asian cultures vs Western Pallet for example.
[3] A device that needs to send "S.O.S" needs maybe 1byte/second or even less. You can't communicate any meaningful information in a seismic-pulse-signal type device, but "SOS" is certainly doable.
nizarmah
TIL about Antenna Theory/Design.
Yeah the human element is the strictest here. From the little research/thinking I did, BLE felt like the most "commonly available" tool we have. But I'm wondering if manufacturing a cheap wearable could also be an option.
I definitely need to do a longer/deeper dive for this project. I overlooked it in the past, thinking people don't need it. But it seems like I just dropped the ball in distribution previously.
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EdwardDiego
Using an AirTag on my dog's collar and WifiMan on my phone to track BLE signals, I could pick it up (just... not enough to interact with it, but enough to detect it above -100dbM) about 8 - 10m with a clear line of sight, and about 2m when she was in dense scrub.
So yeah, I imagine concrete is going to be even worse than a shrubbery, that said, might get some interesting propagation paths if there's metal surfaces in the rubble to reflect waves.
genewitch
My ham license let's me transmit on 2200 meter and 630 meter bands. I'm not allowed to use a 1100 meter or 315 meter dipole, either.
And I can only eirp 1000mW. I mean, legally. I can't eirp anywhere near that can you imagine the losses?
subscribed
I think you can use 5W eirp on 630 meter, at least that's consistent with my band plan :)
It looks that for 600m you could use a vertical wire with a lot of radials :) Maybe with a balloon?
But 2200 would be fun indeed.
genewitch
huh, 5W eirp. Either that changed or my memories did. cool. I also don't remember the 500W PEP ceiling, either. I thought you could drive it however hard you wanted to as long as your radiator didn't exceed [what i thought was 1000] 5000mW eirp.
pizzly
You could make the phones communicate via sound, not sure how it would impact the battery nor its communication range. Lots of details would have to be worked out. You have to find the frequency that communicates the longest. Perhaps do short pulses of sound to save battery life.
genewitch
Unfortunately bass travels the furthest. I can hear cows a lot further away than frogs, and I can hear transport helicopters for miles (miles!)
The problem with bass sounds is ostensibly they're nondirectional. So the ideal sound for a phone would probably be the loudest pink noise they can make without blowing the speaker out.
westurner
What about muon imaging?
What about Rydberg sensors for VLF earth penetrating imaging, at least?
From "3D scene reconstruction in adverse weather conditions via Gaussian splatting" https://news.ycombinator.com/item?id=42900053 :
> Is it possible to see microwave ovens on the ground with a Rydberg antenna array for in-cockpit drone Remote ID signal location?
With a frequency range from below 1 KHz to multiple THz fwiu, Rydberg antennae can receive VLF but IDK about ELF.
IIRC there's actually also a way to transmit with or like Rydberg antennae now; probably with VLF if that's best for the application and there's not already enough backscatter to e.g. infer occlusion with? https://www.google.com/search?q=transmit+with+Rydberg+antenn....
nizarmah
This is pretty cool! I need to learn more about both.
I imagine such fancier tools would be less available among common folks, and more among first responders.
NASA already has the tech to detect heartbeats under rubble using radar [1]. No additional equipment is needed by the rescued. The problem is emergency response can get overwhelmed in large disasters.
If Rydberg sensors would be more common, and new tech is added to mobile devices, this can seriously shift the playing field.
I will look into this, because we need out of the box solutions. Thank you!
[1]: https://www.dhs.gov/archive/detecting-heartbeats-rubble-dhs-...
westurner
"The Dark Knight" (Batman, 2009) is the one with the phone-based - is it wifi backscatter imaging - and the societal concerns.
FWIU there are contractor-grade imaging capabilities and there are military-grade see through walls and earth capabilities that law enforcement also have but there challenges with due process.
At the right time of day, with the right ambient temperature, it's possible to see the studs in the walls with consumer IR but only at a distance.
Also, FWIU it's possible to find plastic in the ground - i.e. banned mines - with thermal imaging at certain times of day.
Could there be a transceiver on a post in the truck at the road, with other flying drones to measure backscatter and/or transceiver emissions?
Hopefully NASA or another solvent company builds a product out of their FINDER research (from JPL).
How many of such heartbeat detection devices were ever manufactured? Did they ever add a better directional mic; like one that can read heartbeats from hundreds of meters awat? Is it mountable on a motorized tripod?
It sounds like there is a signal separation challenge that applied onboard AI could help with.
dimal
This is great. That said, I think that unless Apple and Google install something like this by default, it won’t get much traction, because you can’t download the app when you really need it, and most people won’t think to download it before then.
I just went through Helene in Asheville last year and it was painfully obvious that our cloud overlords have overlooked the offline disaster use case. Basically, when you’re in a situation where you desperately need technology to help, you’re on your own. I was imagining that tools like this would be great, but without the cloud, I was helpless.
Maybe instead of trying to get users to install this, it could be a proof of concept to show what’s possible, and to say to Apple and Google: install this basic lifesaving tool on every phone by default?
nizarmah
This is something I needed to hear for months. Thank you.
I'll work towards that. I'll need to figure out how to prove the poc is useful.
Apple's "Connect to a Satellite" touches on that, but it's not available for most of the world or on old devices. :|
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sneak
Starlink is rolling out direct-to-unmodified-cellphone soon, to provide SMS connectivity to devices in locations that would otherwise be completely offline. It will work on standard, unmodified phones (if they are outside and can see the sky).
Admittedly doesn’t work under rubble, but should work in the usual/general case.
HeatrayEnjoyer
Starlink unfortunately is also not reliable for long-term just outside the US (or even inside).
thenthenthen
How about pivoting to just infrastructureless short messaging (minus the disaster element). Would this get more people on board? (Disclaimer: I have tried and failed…)
Sakthimm
My friend works at one of the world's largest steel plants and recently he was discussing some ideas with me about solving the problem of people disappearing during inspections and being found dead after a few days. Apparently it is a huge problem there that he wanted to build a startup around the tech.
I am saying this because I think your target market may not be people stuck under rubble, but large scale industries, construction site workers, miners, firefighters, who can install the app beforehand. Cheers.
toomuchtodo
Are there any products that can act as a locator beacon, in perhaps a pager form factor? They listen for a signal from a powerful base station at frequencies low enough to deeply penetrate RF opaque material, and upon command, could key up and transmit at max power while using Time of Flight to triangulate (from a network of base stations)? 900mhz comes to mind, but perhaps there are alternate, more optimal frequency bands for this.
It's a local version of https://www.findmespot.com/
nizarmah
Thanks a lot for the insight! You definitely highlighted an aspect where this tool could be monetized to fund the development of an open source project like Igatha.
Sadly today, money and connections are needed for r&d and distribution. And having a market that buys a tool like this in certain circumstances can seriously contribute to finding/building publicly available solutions.
financetechbro
I’ve recently had to do a deep dive into construction tech + frontline (deskless) worker tech and there is a lot of potential in this space. Very underserved market. Lmk if you’d like to chat and I can provide some insight on what we’re seeing here in terms off greenfield opportunity
nizarmah
I would definitely like to chat about it. Right now, it's the main picture in mind towards getting some funding to push this project forward. So, I'd love to learn more about it.
subscribed
I can imagine a firefighter, miner or steelworks worker relying on the smartphone in emergency. Like, seriously, a miner, half of a mile under the rock.... Carrying smartphone?
Heavy duty wearable tags and a dense network of wall-mounted relays pinging them and triangulating 24/7 can be the only solution. Sure you can use BLE beacons for that, and this is being solved with multiple competing products as we speak (look up "locating objects in warehouse"), but specifically for the human safety applications, they would have to be imposed by the regulators. Workforce is seen as disposable and nothing short of laws and regulations is going to force employers to improve safety.
6footgeek
Ex miner here (grasberg, Indonesia) - yes, we all had smartphones, at all times, and yes, we rarely had signal but if you went up to the surface / anywhere with signal, you would want your phone, so we all carried them.
defrost
The majority of the worlds miners work above ground - they still run the risk of stope (wall) collapse, but they're unlikely to find themselves under half a mile of rock.
In Australia, open-cut mining dominates coal production, accounting for over 80% of the total, while underground mining's share has decreased to around 15%. Open-cut mining is generally more efficient and cost-effective, allowing for higher recovery rates and larger-scale operations.
It has been estimated that more than two-thirds of the world’s yearly mineral production is extracted by surface mining. There are several types of surface mining, but the three most common are open-pit mining, strip mining, and quarrying. These differ from one another in the mine geometries created, the techniques used, and the minerals produced.
Like anybody else in the modern world, it's hard to pry smart phones away from mine workers ...
Miners warned to limit smartphones in the pit (2013) - https://www.itnews.com.au/news/miners-warned-to-limit-smartp...
pjs_
This is cool! I have been really enjoying using Meshtastic and LoRa lately. It feels like a blessed relief from the toxic swamp of the regular internet. I love pinging stupid radio messages across the bay without depending on any third-party infrastructure. Maybe in addition to the literal rubble of a life threatening disaster we can use tools like this to dig ourselves out from the psychological rubble of the information superfund site we have built for ourselves
noman-land
You got anyone pinging you back? I can't convince any of my friends to care.
genewitch
I'm this way with trying to convince random people on the internet to chat over fldigi on HF frequencies. Hellschriber is awesome.
noman-land
TIL!
---
Fldigi is a free and open-source program which allows an ordinary computer's sound card to be used as a simple two-way data modem. The software is mostly used by amateur radio operators who connect the microphone and headphone connections of an amateur radio SSB or FM transceiver to the computer's headphone and microphone connections, respectively. This interconnection creates a "sound card defined radio" whose available bandwidth is limited by the sound card's sample rate and the external radio's bandwidth. Such communications are normally done on the shortwave amateur radio bands in modes such as PSK31, MFSK, RTTY, Olivia, and CW. Increasingly, the software is also being used for data on VHF and UHF frequencies using faster modes such as 8-PSK. Using this software, it is possible for amateur radio operators to communicate worldwide while using only a few watts of RF power.
Its_Padar
Another interesting protocol that supports LoRa is Reticulum, which uses an announce based system for bandwidth efficiency instead of Meshtastic's flood based routing.
nizarmah
TIL thanks for sharing those!
weikju
What's not clear to me is, who's listening? Like if I install this app and I get buried under a crumbled building and send out the SOS signal... Are there any receivers???
nizarmah
People, nearby, with the app installed who open it during a disaster. That's why it needs to be in more hands.
Ideally, there would be an option to have your phone "listen" in the background and notify you if anyone needs help. I haven't added that yet.
For now: let's say I'm in a neighborhood. An earthquake happens, a building collapses. I have the app installed and I'm fine. So, I open it and I get close to each building and check if there are any survivors under it.
You'll keep broadcasting, until your battery runs out. It's not heavy on the battery, so it can broadcast for a while.
I'll clarify that in the readme.
boc
Check out the tech behind avalanche beacons for some inspiration. They are meant to locate bodies buried deep in snow debris fields within a meter precision. You have to also have a beacon to search for another beacon.
eddythompson80
Surprising as it may seem, avalanches are easier to avoid [1] and easier to handle it comes to communication[2]. To an extent of course[3].
[1] I used to be terrified of the concept of an Avalanche. However, at the end of the day you're only exposed to an Avalanche if you choose to be or live next to a large mountain in the winter. It's not even like Hawaiians living next to an active volcano. All you have to do (in terms of living) is to move away during Avalanche season. Hawaiians atleast have the excuse of "it hasn't erupted in 10 years"-maybe. THe other example is if you're a skiing/winter-sport enthusiast (like me). And you simply balance your chance of an avalanche vs the reports and "how much fun it sounds to ski with your friends"
[2] If you find yourself in an avalanche situation, you need/must do your best to "swim" to the top of the avalanche. There is gear that can help you do so outside of beacons or "signal based" notifications. Once you've established all those unfeasible, you're left with the same tools a "sudden earthquake victim" is up against. You still have the upper hand because a simple handheld transceiver (from like Icom, Kenwood or Yaesu) will have 100x the range through snow vs one through liquid water or concrete.
[3] Physically speaking: ice is eventually going to behave like water under enough depth. I think.
[4] Avalanche Gear example: https://alpenglowsports.com/collections/avalanche-safety
INTPenis
Satellite based emergency services are already enabled in recent Android phones.
I know that only because recently I have been getting a notification on my Pixel 9 Pro that Satellite based emergency services are going in and out of coverage for some reason. I never even knew it existed until my phone told me it was down lol.
At this moment they only cover some countries, but it might be well worth focusing on building out this tech instead of trying to make something new.
nizarmah
It's awesome that it's coming to Android as well. I was mind blown when I got it on my phone traveling between Spain and Portugal by car.
It's hard to find a one-size-fits-all solution. I don't know if satellite coverage would still be available under rubble. It's definitely valuable in other situations.
The country coverage is a huge part. My country will likely not get satellite coverage in the next 5 to 10 years. Such countries is where disaster response is worse and infrastructure is more prone to failure.
lunatuna
As a thought, not tested, using wifi probe requests might be better through more dense material scenarios. Using a specific AP probe request "SOS Request" from the device would help discover over all the other AP requests that others are throwing. No idea if iOS or Android would let you hijack that process.
This is a bit more extreme, but some type of triangulation from multiple rescuers could be useful in closing in on a spot.
This is really interesting and thanks for sharing.
nizarmah
I collected a list of alternative options for signals that I'll be looking into [1]. I included wifi probe requests as well. Thank you so much!
rapjr9
BLE might be useful above ground in some situations, e.g., a person who is unable to stand and is located in a large field of tall grass, or someone who is hiding from an attacker and wants to silently request help.
For the specific case of burial under rubble it might be better to work on sensing sounds rather than using radio broadcasts. If the person can move they may be able to tap on concrete with another piece of concrete. Using three or more phones (plus BLE or WiFi for timing coordination) placed on the rubble it might be possible to triangulate the location of the tapping. While there are professional (expensive) versions of this (like the heartbeat detector mentioned above), giving the capability to everyone could be useful. Adding the BLE emission/detection couldn't hurt and when the trapped person runs the app it could give them instructions to maximize their chances of detection. For tapping those instructions might be to tap three times once every five minutes to minimize the physical energy required. That would mean the three sensing phones would need to wait 5 to 10 to 15 minutes to do detection and acquire a location. Tapping on stones could work by itself since people can put their ears to the rubble and listen for the tapping, so the main benefit of the app might be just to tell the person what they should do in their situation (tell the trapped person to tap 3 times every five minutes, tell the rescuer to listen for 3 taps occurring every five minutes, providing a timer to indicate the 5 minute intervals could be useful too). Five minutes might not be optimal, some research would be needed on that, and it may depend on the energy level of the trapped person so perhaps the sensing cell phones should be left in place for hours or days. Ideally all phones would have this as an emergency app that would provide advice and help with BLE beacons, timers, cellular calls, sensing, and whatever in any situation.
In general this seems like a difficult problem and worthy of some extended research.
nizarmah
+1 to sound, I'm planning to research that thanks to all the helpful HN comments like yours :D
I find the "instruction app" a little limited because a person needs to be conscious, they need to be calm and collected to remember to open the app, and their phone needs to be accessible.
In its current state, providing instructions is better than just broadcasting BLE which will be weakened and lost by rubble.
In my country, a lot of first responders still rely on asking people to scream if they can hear them. Anyone unconscious would be discovered days later...
There has to be some way of providing an automated signal of life.
The comments about the physics limitations are pretty awesome. They make me wonder if we can assist it in any way... I learned about passive resonators recently. I know they have a short distance transmission, but maybe if they were part of the building material?
I need to start by learning more about the physics. I know I'm limited by it, but maybe there's window we can walk through instead of the door.
np1810
Cool idea and this was nostalgic as well... I created a similar application to communicate and send beacon signals over SMS (using Twilio) without Internet (as internet went down) during emergency SoS situation motivated by 2015 Chennai floods...
Suggestion: You can possibly try if you can use OpenHaystack [1] to send some "unknown tracker found nearby" alert to any nearby iPhone even if the receiver device doesn't have your app installed or use the FindMy network to send arbitrary data for your app's communication. [2]
ashoeafoot
Silica gel was at the core of a cool water collection contraption to collect moisture in the dessert . Now add this and the ability to sinter sand together in the dessert and you could print windstills with robots.
axegon_
There is one thing that could make this insanely valuable. The bad news is that this thing is outside your control: No phone that I know of ships with a LoRa chip. Though to be fair, the only reason why LoRa (and by extension LoRaWAN and Meshtastic) are reliable and robust is precisely because they are not common at all.
A couple of months ago, I built this app to help identify people stuck under rubble.
First responders have awesome tools. But in tough situations, even common folks need to help.
After what happened in Myanmar, we need something like this that works properly.
It has only been tested in controlled environments. It can also be improved; I know BLE is not _that_ effective under rubble.
If you have any feedback or can contribute, don't hold back.