Sorry, I thought the AQI complication (which is also new) was the Noise Complication. It seems like, at least on the older watches the Noise detection will happen on the background since there is an option to turn it on the Watch App.
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And this is the calculator App on my S2.
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That might be the case. I have a series 4 and the noise app and complication are available and functional for me.
Thanks you thunder025! I was able to find it, it looks like it's only available within the Notification section right now, not an app or anything. It's likely they haven't put the app into play just yet.