OK Google function is what allows us, through voice commands, operate the terminal, do Google searches or even activate the alarm of our smartphone. If for some reason does not work, read attentive the following recommendations:
Go to the S Voice application, and the settings must disable the voice option Awakening.
Then, in Settings -> Language & input -> Google voice typing -> Detection Ok Google, you must have activated "always on", despite the redundancy. In doing so, restart the terminal.
If nothing works, the last option is to restore the phone factory, unfortunately.