Source: Simon Willison's Weblog
Retailers and venue operators are embedding inaudible high-frequency sounds in stores, malls, and public spaces to track customer location and movement patterns. Most smartphones passively listen for these signals without user awareness or consent. This moves beyond passive data collection (WiFi, Bluetooth, location services) into active behavioral surveillance that occupies a legal gray zone, making location tracking nearly impossible for consumers to opt out of even if they disable GPS. Brands gain granular foot traffic analytics. Consumers lose the assumption that their physical movements through public space aren't being logged and correlated with their purchases.