While a noise gate is an obvious starting point, I suspect that much smarter filters are possible. A wide range of design choices are possible that trade CPU <-

While a noise gate is an obvious starting point, I suspect that much smarter filters are possible. A wide range of design choices are possible that trade CPU <-> complexity <-> accuracy. If a high error rate (including "no data") is acceptable, a filter might simply default to "off" when any unusual condition like "noise gate has been on continuously for 15 minutes" is detected. If I was designing this kind of spyware, I would put a hard limit that cuts off uploading any "extra" data after sending some low multiple of the "legitimate" data.