
The scientists tested their hypothesis by replicating the "chirping" from an AP video using two ultrasonic emitters that combined tones, one at 25kHz and another at 180Hz. That produced a similar-sounding 7kHz frequency with ripples of sound at an even 180Hz spacing. The team even built a device that would simulate eavesdropping by playing a song instead of the 180Hz tone. more
Security Scrapbook fans knew this might be a botched spying attempt, and how it worked, last August. ~Kevin