Device-to-device audio communication (think QR codes, but made out of sound) seems very underrated. Much better UX than QR codes or NFC because you don't have to worry about putting your phone in the exactly right place or pointing it in the right direction.

Anyone here with more detailed takes on this?

I built an app that did this about 10 years ago that did offline TXs. issues we ran into:

- poor microphones at the time on android meant (iPhones were fine) we were relegated to them 
- there’s a lot of noise in the world
- bit rate on audible sound spectrum is slow

creating and destroying; built flying cars & autonomous vehicles, now building /faust, more here: /july, web: july.rocks

NFC, audio, wifi like networking is two things at play:

1) the comms protocol itself. For wireless: NFC is 13.56MHz, Wifi is 2.4 GHz etc, or wired like UART I2C etc and 

2) data exchange format protocol we all agree upon (NFC forum tag type and ISO 14443A) 

If we did audio we’d have to agree on both

There’s ofc a long history around 802.11 and it’s variants 

Anyway not to say that device to device data communication through sound waves won’t work but since sound waves are slower than EM (and more prevalent EM radio equipment than high end sonic chips) it’s going to be a bit slower - needs justification

But also this is 10 yrs ago and I find the ideas around use cases for crypto are interesting

More things:
- high frequency inaudible sound above 20kHz is ideal; but not all speakers support it or not all microphones support it
- doing the decoding of msgs took more to compute than was a good UX
- also had to be loud in order to actually get messages through