ggwave

ggwave is an open source library where to two devices, can communicate.
It's an effective way to transmit information to/from other device in a controlled environment.[^1]

While it's slow, and require setup, the main advantage is that when a device send information to the other; you could interrupt the information because you can hear it!

[1] Link to project on Github, https://github.com/ggerganov/ggwave