Wouldn't that destroy your battery life?
[1] http://21stdigitalhome.blogspot.ca/2013/06/vcp200-voice-reco...
the downside was power usage. Motorola made one that was power efficient, used by nokia in the 90s and its pretty much the same chip in google's phone line today (just even more power efficient).
division is under lenovo now
Your phone reads sensor data as a base state.
It has a battery impact but much less than sending all the voice data continuously to a server somewhere. The biggest battery killer would be the wifi or 3G transmitting non-stop in that case.