I think there's a broader indication of an arms race between noise cancellation systems and things that want to be heard, like advertising. And this just-happening-to-exist bandpass that the DuoBell is depending on could easily become collateral damage in that fight.
I was going to make a joke about advertisers working in some kind of ultrasonic modulation to their audio so it breaks ANC (I'm aware this wouldn't really work) but then thought, whats more likely, advertisers doing that, or advertisers partnering with 80% of ANC chip makers to just let them by-pass with specific tone markers...
Then we'll be hacking our headphones with specific 3d printed clip-ons that involve a particular brand of coffee filters that happen to attenuate the "clear freq" enough for the headphones to miss it.
