your first point coupled with diminishing free air range in bands above 40kHz makes this hack seem like a futile attempt to simply gather as much data as possib

your first point coupled with diminishing free air range in bands above 40kHz makes this hack seem like a futile attempt to simply gather as much data as possible, as low or uncorrelated as it might be. Some phones might be more cappable than others, however, and air is dense enough for several meters of significant ultrasound transmission at low power. With e.g. Samsung TVs always listening, I wouldn't be surprised if they optimized the speakers and micros in that regards, while benign applications aren't out of the question either. The second point however is an overly broad generalisation disregarding the technical inaptitude of the target group of such apps (wherein I might include myself).