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

(github.com)
158 points nizarmah | 2 comments | 01 Apr 25 21:58 UTC | HN request time: 0.401s | source

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.

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eddythompson80 ◴[02 Apr 25 01:51 UTC] No.43553008[source]▶
> 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.

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westurner ◴[02 Apr 25 03:04 UTC] No.43553294[source]▶
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....

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1. nizarmah ◴[02 Apr 25 09:33 UTC] No.43554997[source]▶
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-...

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2. westurner ◴[02 Apr 25 13:36 UTC] No.43556519[source]▶
"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.