I just realized that "hey Cortana" does not work in windows 10 mobile builds 10166 or 10512. I remember when I had 8.1 with denim update it came to my Lumia Icon but now it doesn't work. I found the setting for it in extras but when I click on it, it says "this feature is not available for your phone." Does anyone have any information on this or if it works for you? I couldn't find anything on it after a search.