GTG-ZERO Mobile microphone jammer - The StealthMall
Understanding the Effectiveness of Ultrasonic Microphone Jammer
GitHub - allisonburtch/micjammer: Schematic for an ultrasonic jammer that produces noise at 20kHz, around the range of the iPhone MEMS microphone. It's a way to non-invasively mute your microphones.
Stealth Personal Microphone Ultrasonic Audio Phone Jammer - Etsy Australia