Comment by 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.