Ultrasonic Beacons: How Your Phone Hears Ads You Can’t
An ultrasonic beacon is a short audio signal. It lives above normal hearing, often above 18 kHz. Speakers in TVs, kiosks, or stores can play it. To you, it sounds like silence. To a phone microphone, it sounds like data. The beacon often carries a simple ID. That ID links to an action, such as logging a visit or triggering an ad.