This is a command-line program that encodes short messages/data into audio and plays it via the motherboard's PC speaker. To use this tool, you need to attach a piezo speaker/buzzer to your motherboard. Some computers have such speaker already attached.

You can then run the following command:

echo test | sudo r2t2

This will transmit the message test via sound through the buzzer.

To receive the transmitted message, open the following page on your phone and place it near the speaker:

https://r2t2.ggerganov.com

Applications

This tool can be useful when you need to transmit data from air-gapped machines. The hardware requirements are very low-cost - you only need a PC speaker. Automated scripts can be configured to periodically emit some data about the machine, which can be received by someone nearby running the r2t2 receiver application.

Requirements

PC speaker / buzzer attached to the motherboard.

Here are the ones that I use:

Img. Left: PC speaker plugged into a motherboard. Right: two PC speakers with a coin for size comparison

Unix operating system
Add the pcspkr kernel module: sudo modprobe pcspkr
The program requires to run as sudo in order to access the PC speaker

Build

git clone https://github.com/ggerganov/ggwave --recursive
cd ggwave
mkdir build && cd build
make
./bin/r2t2

Acknowledgements

Thanks to Radoslav Gerganov for this cool idea!