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Comment by thenewnewguy | Hacker News Reader

That's a pretty incredible claim, you got a source on that? My searches can't find anything.

While not this exact claim, years ago I wrote an app for a TV show to detect ultrasonic tones embedded in episodes of the show. While not solely for tracking (it was to sync a clock to the episode you're watching), there were special tones to trigger ads.

I could easily see this being expanded upon and included in a tracking SDK.

How did you get around the permission to use the microphone restriction? And if it is in use the status bar turns red on iOS.

>How did you get around the permission to use the microphone restriction?

An app can already have recording permissions for legitimate reasons.

>And if it is in use the status bar turns red on iOS.

It only turns red if a background app is recording.

> How did you get around the permission to use the microphone restriction

The app asked for permission as usual.

"Marketing Beacons": https://www.wired.com/2017/05/hundreds-apps-can-listen-beaco...

I can't help you about that but it reminds me of the Spanish Liga listening to their app to look for pubs that were illegally streaming their matches.

https://www.theverge.com/2019/6/12/18662968/la-liga-app-ille...

https://amp.theatlantic.com/amp/article/416712/

Not Nielsen related per se, but this technique has been circulating for at least a few years. That's a 2015 article.

The technology is called ultrasound cross-device tracking (uXDT) and companies like SilverPush are doing it. There is an ever-growing amount of android apps that contain this tech. DDG'ing should yield quite a bit of interesting articles about this practice.

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