How to enable dictation by voice on OS X? I want to be able to say something like, "Start Dictation," to turn on OS X's Dictation feature, instead of having to double-click the fn key.

In System Preferences -> Accessibility -> Dictation, there is an option to "Enable the dictation keyword phrase." Here is a screenshot of this menu:



I have enabled this option and tried various phrases and the dictation has not been turned on once.

I'm not sure if this is related, but I have installed the "Enhanced Dictation" data:



Within the "Dictation Commands" menu, I have all "System" commands enabled, including the "Start Dictation" command. Screenshot:



Incidentally, the "Stop Dictation" command works perfectly.

Has anyone managed to Start Dictation by voice command?

(2013 rMBP) -- (OS X 10.11.3)
Look at your first screenshot.
Enable the dictation keyword phrase

To activate dictation by voice command, just speak the phrase "Computer Start Dictation"