I don't work on such projects, but on other ML projects, and I suspect the answer is: training data. There are many, many, many samples of people saying the ap

I don't work on such projects, but on other ML projects, and I suspect the answer is: training data. There are many, many, many samples of people saying the approved trigger phrases. Many, many, many samples. To use your own custom trigger phrases, you would likely need to say it thousands of times to being to approach the accuracy the current systems ship with out of the box. Maybe tens of thousands. That's just my conjecture, though.