Larry has a Samsung Galaxy Gear watch, one of the first devices. He uses it with the Galaxy Note 4. It's such a huge device so the watch saves him from having to use the Note all the time. Leo says he agrees and used it to take pictures while flying along with a zip line. The watch is great. However, the Note 4 went through an update and then the "OK Google" function didn't work. He went into the voice settings and they're gone! It works within the app, but it won't work globally.
Leo says that's up to the launcher and one of the reasons why Leo doesn't use Samsung's Touch Wiz launcher, because they want people to use their S Launcher instead. He uses a third party launcher and tells it to listen globally, then he disables S Launcher. The one thing he'd lose is that only S Voice will respond when the screen is turned off.
Doctor Mom says that it's in the language and input menu of the settings. Go into Speech, and then check off "enhanced Google Services." That brings in the global settings.