In June 2017 Apple hired Stanford's Dr. Sumbul Desai to work on Health Services for Apple Watch. Two years later Dr. Desai intro a few new Health Apps for Apple Watch during here WWDC 2019 keynoted segment. One of the new apps introduces was the "Noise" app.
Below you'll find the WWDC 2019 Keynote that has been set to begin when Dr. Desai began talking about hearing health and introduced the Noise app. This segment runs a little over a minute. You can stop the video after that segment ends.
Last Tuesday the U.S. Patent and Trademark Office officially issued Apple a granted patent for this new health feature titled "User interfaces for monitoring noise exposure levels." Apple kept this app secret as they're on record as never having filed a traditional patent application under "Apple."
One possible explanation for this is that Apple may have acquired the patent, as the sole inventor is listed as Nicolas Felton, an information designer who has no record with Apple on his LinkedIn account.
Apple's patent FIGS. 6A-6L illustrate exemplary user interfaces for monitoring noise exposure levels with two of the patent images from that group presented below.
Apple's granted patent covers 54 pages of specific Noise app patent figures with many pages covering dual images. You could review all of the patent figures found in granted patent 10,764,700 here. The Noise app images begins on page 15.
Apple's patent notes that this app is for Apple Watch (a smartwatch) but also lists that it could be for their iPhone, iPod touch and the iPad even though it's currently limited to the Apple Watch. In fact, the patent also mentions that it could be found on MacBooks (laptops) and the iMac (desktop).
While Apple always likes to ensure that their inventions are never limited to one application or device, it doesn't mean that it's a guarantee that it will ever go beyond Apple Watch.