A short message crosses from one device to another as sound, above 16 kHz. No network, no pairing, nothing to point at. The transmitter does not know whether anyone is listening and loops forever: a receiver that joins halfway still gets the whole message.
The repository ships only the demonstration key. Generate your own,
install the same key in the device firmware, and keep operator.json private.
Turn the volume up and hold the devices half a metre apart. The signal sits between 16.4 and 18.8 kHz: nearly inaudible to an adult, audible to children and animals.
Each square is one block of the message. They light up out of order: what arrives is not "block number 7", it is a combination, and the message dissolves out by itself as the combinations simplify.