You can send text-based messages to nearby friends using sound.
This is a demonstration of how acoustic modems operate. Note, there is no encryption or security associated with this system at present. It is a simple message broadcast system that encodes a textual message into chirps which are then played through the speaker.
Chirpr uses Binary Orthogonal Keying (BOK) and Chirp Spread Spectrum (CSS) which translates to using up and down linear chirps to transfer information.
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