[ksangeelee]

I searched for microphones with an integrated low power DSP, and the first hit [1], from 2016, described a device for always-listening voice activation using an EEPROM configured DSP that claims to consume 0.4mW at 1.8V (0.22mA). That seems astonishingly low, and would be unnoticeable in terms of battery drain on a modern smartphone.

While the article describes a 'trigger to activate' scenario, I guess the DSP could also be configured to output data at an earlier stage in the chain for post-processing on a server. The volume of data would be orders of magnitude lower than sending raw waveforms. Of course, this would introduce the need for some memory for buffering, which eats into the power budget, but having read about this device, I'm pretty convinced that it's technically feasible.

Whether or not phones actually do this at a low level is another matter. It would be an interesting experiment to graph the current draw from a sleeping phone's battery while conversations were being spoken into the mic.

[1] https://www.sensorsmag.com/components/mic-hears-all-all-time