Also, keyword detection algorithms are different from general purpose speech transcription algorithms. The general pattern is to write a specialized model that'

Also, keyword detection algorithms are different from general purpose speech transcription algorithms. The general pattern is to write a specialized model that's really good at robustly identifying the key phrase, run that continuously, then trigger recording and full transcription only when the key phrase is heard. Those keyword identification algorithms can be implemented at the hardware level. I believe this is done for specialized devices like Echo and Kinect, not sure how phones do it.