The app uses the watch's built-in microphone to measure the decibels at concerts, theaters, parades, construction zones and other loud situations that generally aren't good for your ears.

If you think you may be in an at-risk environment, you can open the app and check the decibel meter, which adjusts in real time. 

Noise app detects loud environments and notifies you when it thinks you may be at risk for hearing damage. It is still in the testing phase.