Sorry but I found this to be very disappointing scarebait from Ars, who I expected to have higher standards. It doesn't explain how common this is yet the title makes it sound like it's super prevalent. (not to mention we're already being tracked in other ways that are worth worrying about more) It does a horrible job at explaining what's actually going on and why advertisers might use this instead of alternatives, in fact I still don't know. (something about every ad containing ultrasonic sounds and everyone making their app use the microphone to constantly listen for them—I get that it's a real thing but sounds way too contrived and complicated to be common) The title is also super clickbait and I wouldn't characterize it as the good type of FUD. The solution they propose is a proof-of-concept patch, so not an actual functioning solution (and their extension is supposed to block ultrasonic frequencies, but advertisers will just move to audible frequencies then and mask it as music). Even if they improved the title, the article itself is flawed and is predicated on making us scared of this, even having the gall to say "Now that you’re sufficiently concerned". C'mon Ars... I get wanting to point out troubling practices and increasing awareness, but at least do it in a less knee-jerk and more informative manner.