Now my both launchers, SquareHome and ssLauncher, starts to support this feature.
Turn on the 'OK Google' option in the preferences and make sure 'Google settings' are set correctly.
1. Turn on 'OK Google'
|Preferences in ssLauncher|
|Preferences in SquareHome|
2. Tap 'Google Settings' and make sure Google Now and "OK Google" hotword detection are on.
If you don't have the "Ok Google" hotword detection option in Voice settings, try to change the Language to English.
3. Back to the launcher and say 'OK Google'