I wanted an answer to a boringly practical question: what if the network is gone, but the speakers and microphones still work? SignalHop is an acoustic modem and mesh prototype that moves tiny messages over ultrasound instead of Wi‑Fi or Bluetooth. What it actually does The current build uses: FSK tones at 18 kHz and 20 kHz 48 kHz sample rate a 4 up-chirp sync preamble frames with payloads up to 255 bytes a WAV/audio runtime for encode/decode and round-trip testing That makes it useful for emergency text, sensor payloads, and low-bandwidth status updates. Not glamorous. Very useful. The measured part From the current proof pack: Metric Value Encode latency 16.634 ms mean Decode latency 713.028 ms mean Round-trip true Payload tested 77 bytes Max payload 255 bytes The decode path is slower because it scans the full signal with correlation. That is fine for v1. The important part is that the numbers are measured, not imagined.…