This is a handy feature available in Android phones with at least version 4.1 of the OS. You can use different voice commands to call people, text people, add a reminder, search the web, get direction etc. If you are interested in turning this feature on or off, then it is accessible from App Drawer > Google Settings > Search & Now > Voice > "Ok Google" hotword detection.
Here's how you turn on or off "Ok Google" hotword detection in detailed steps:
- From your app drawer, access an app called "Google Settings". Remember that this is not your main phone settings.
- From Google Setttings, tap on "Search & Now".
- In the next screen, under "SEARCH & NOW CARDS", tap on "Voice".
- Then, tap on "OK Google" hotword detection.
- In the final screen, you can turn this feature On or Off by tapping on the On/Off slider.