Question: I'm looking to add voice commands to an Android App that will be running on a tablet as a kiosk. I don't want the user to have to push a button, because the user is doing something more important (e.g. driving a car, flying a plane, or performing brain surgery) and the command could be completed by a single button push.

I see tutorials describing how to add speech to text and have the user push a button and get the text, but nothing allowing the wake word "Okay, Google" to start the voice recognition (much less a custom wake word).

I looked at using the Google Voice Actions to start with "Okay, Google" and then send something to my app (register an intent), but that has to be trained to one specific user (at least for the tablet I tried it on). I'll have different users every day (maybe more than one a day) and no opportunity for training the device.

I've worked with CMUSphinx and found it to be too unreliable for spotting a wake word.

Is there a way to add "Okay, Google" as a way to start listening to text inside my app?

Answer: 
Got it working using PocketSphinx for offline wake work recognition and then I hand the microphone over to IBM's Watson's Speech to Text software that works over the internet and comes back with pretty reliable results.
Unfortunately what you are trying to achieve is not possible. If I understood correctly what your concept: a 3rd party app will awaken the devices and act based on a set of commands (from a security point of view this is very bad).

The closest you can do is follow the Voice Actions Api - <https://developers.google.com/voice-actions/system/>