We demonstrated this in 2003 using the smartphones of the era (they didn’t have good filters, so you could detect ultrasound quite easily). See https://anil.re

We demonstrated this in 2003 using the smartphones of the era (they didn’t have good filters, so you could detect ultrasound quite easily). See https://anil.recoil.org/papers/audio-networking.pdf https://anil.recoil.org/papers/audio-networking.pdf sec 2.1 for the 2003 paper and some ancient videos at https://anil.recoil.org/projects/ubiqinteraction https://anil.recoil.org/projects/ubiqinteraction if you want some Nokia nostalgia :-)