Show HN: Offline SOS signaling+recovery app for disasters/wars

> 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.

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.

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?

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.

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

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.

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???

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.

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.

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.

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.

[delayed]

The EU is mandating Apple to implement WiFi-Direct https://www.ditto.com/blog/cross-platform-p2p-wi-fi-how-the-...

WiFi doesn't fare any better than BLE under rubble unfortunately, but WiFi is going to be a useful technology to build disaster response tools in general

Have you considered making the app to take a GPS reading then turn off the GPS to save battery life? If the person say is trapped in rubble they likely not going to move afterwards thus you can relay this location information to nearby receivers.

This is awesome. Technology put to good use.

Can voice be transferred? Message be recorded and rebroadcasted?

What about making the device vibrate SOS pulses. The person at stake might not have the strength to tap or bang, may be able put the phone on a metallic surface and send vibrations?

It would be nice to have a button to play a loud sound. A common use case is to play it when you are under ruin and you hear rescuers close to you. If the rescuers heard a loud sound, they can locate you quicker.

I don't know the amount of battery that is necessary to do that.

This is great. Is there a version of this that does p2p off-grid messaging? Use cases from: 1. Coordination between group members during camping in the wilderness. A mesh solution that works across iOS and Android would be ideal but mesh isn't a hard requirement either. 2. Messaging within a group who's flying together but across different seats/sections at cruising altitude in a long haul flight.

Do smart phones support "LE Long Range (Coded PHY, S=8)" Perplexity says it can transmit up to a 1km in ideal conditions. Otherwise it's 10-30m indoor.

How many people in my city or neighborhood must install the app (and use it, watch notifications) for it to serve its purpose?

It of course depends on the disaster, but in case of war this app can be used to find survivors for purposes other than saving them.

Great idea though.

I feel like this has some potential overlap with the PulsePoint app (that one is for CPR/AED emergencies rather than large scale disasters), so that could be a potential partnership to look into.

Might be rough on battery life, but perhaps pulsing an SOS with the flashlight?

There's LoRa runs on 450/900 MHz with complete stack for transmitting and relaying messages. There's even modern encrypted protocol (meshstatic) built on it.

Not really high tech but worth mentioning that some shortwave portable radios (a world radio receiver is an item you should have in your earthquake emergency supplies) have a portable blare out alarm horn function to signal your presence to first responders.

Although it has the obvious limitation that you would have to be within arm's reach of it before you were to be trapped in a collapsing building, and sound can travel sufficiently under rumble.

this is good but ideally people want this app/platform to be embedded in hardware/OS level

From "Homemade AI drone software finds people when search and rescue teams can't" https://news.ycombinator.com/item?id=41764486#41775397 :

> {Code-and-Response, Call-for-Code}/DroneAid: https://github.com/Code-and-Response/DroneAid

> "DroneAid: A Symbol Language and ML model for indicating needs to drones, planes" (2010) https://github.com/Code-and-Response/DroneAid

> All but one of the DroneAid Symbol Language Symbols are drawn within upward pointing triangles.

> Is there a simpler set of QR codes for the ground that could be made with sticks or rocks or things the wind won't bend?

Kudos for all your hard work! Getting to 1.0, getting on the app store, and making something that should be on all phones - you did awesome!

I would change your license so it can’t be stolen by Apple. At the very least they need to buy it or hire you as employee.

Okay, what is "disaster detection"? I'd really prefer my phone not chirp noise over Bluetooth channels if I don't notice and respond to a notification in time.

Would be nice if the readme included the current method to detect disaster and the nature of the "SOS" signal. Is that something Bluetooth has a behaved protocol for, or is it really just chirping?