Ok Google from outside the app

After I upgraded my system on my Meizu MX5, I see no option in Google App to turn on Ok Google detection from outside the app (Settings > Voice > "Ok Google" detection > and here I have only From the Google app). In Google support website I see that "**For certain devices,** you can also change some settings to turn on "Ok Google" detection outside the Google app". So what are these "certain devices"? I have Android version 5.1. Why can't I use Ok Google from outside the app although I could use it before updating my system? **edit:** I opened an issue here: OK Google options missing