alt Hacker NewsThanks, very interesting. Basically the authors blast high-power (~92 dBA) ultrasound around 25kHz and hope that microphone non-linearities will overwhelm the audible signal.
This will sure make all the dogs in 20m radius mad. Hence the solution for the stealth recorder -- bring a dog, then complain about the ultrasound jammer (or at least to be aware of a jammer)
From the paper, it looks like the authors did not consider safety of animals, only human hearing safety.
As someone frequently annoyed by those stupid bird/deer/insect ultrasound emitters I hope this doesn't become common, with my luck I'll be able to hear them.