I actually experimented with this using ultrasonic signals (most people can't hear above ~16-17kHz), and with very simple modulation was able to transfer ~30bps. Was a very fun proof of concept, using just a cell phone and a speaker! I think the idea is great and there are many applications for it.

In this one I embedded the signal into a song, and then the phones would parse the modulated data to all synchronize together and create an ad hoc light show with the flashlights!

Sigh... you're making me want to put together a laptop/mobile version of PSK-31[1], just to see if I can do it.

[1] http://rsgb.org/main/get-started-in-amateur-radio/operating-...

"Wireless" transmission of sounds through the air to achieve some programmatic purpose is relatively widespread, although not very well-known. The air is a noisy medium, so ultrasound is often used to move the sounds squarely out of the frequency range that humans can produce or hear, but usually keeping it within ranges that off-the-shelf microphones can record and speakers can produce.

In recent years, one particularly significant contributor is Boris Smus [1] who released some example code in 2013 and went on to develop the Google Chromecast's ultrasonic pairing mode [2].

Ultrasonic networking has also been leveraged by tracking apps and SDKs [3], and has occasionally featured as a product pitch [4]. It also pops up every once in a while as a proof-of-concept, Show HN, or github code dump -- it's one of those "I can't believe this isn't done more often, so I'm gonna do it" ideas whose deployment is actually more widespread that most people suspect.

[1] http://smus.com/ultrasonic-networking/ [2] https://gigaom.com/2014/06/26/chromecast-will-use-ultrasonic... [3] https://news.ycombinator.com/item?id=13337949 [4] https://www.chirp.io/

Yes, it is very much possible. Take a look here: https://github.com/romanz/amodem/blob/master/README.rst

The transfer speed and noise are, obviously, too low/high to make any practical use out of this, but it's a cool experiment anyways.

I remember reading about a exploit/virus for BIOS that could coordinate an attack with infrasound, but I can't find any link.

It never really panned out: https://en.m.wikipedia.org/wiki/BadBIOS

Here's a real exploit instead. Audio-only attack revealing RSA private keys in GPG!

https://www.tau.ac.il/~tromer/acoustic/

That's basically what Google Nearby uses - one of it's options is to signal to near devices over ultrasonic audio. In fact it looks they are even using it for a payment system http://www.dailymail.co.uk/sciencetech/article-4896748/Googl...

Not sure what the actual technical specification for the method is.

There's a constant noise for data after the connection has been negotiated. I'm not sure how loud it would have to be to work.

I do remember hooking up two modems directly with a phone line, turning off dial tone detection on the answering modem and issuing an ATA on the answering modem and a ATDT on the calling modem and negotiating a connection that way. It still was only able to transmit at roughly 3 KB/sec.

That's how the early modems worked, although at a very short distance: https://en.wikipedia.org/wiki/Acoustic_coupler

Reminds me of this DEF CON talk: https://www.youtube.com/watch?v=gFTiD7EnVjU