Being a very light sleeper myself I have often wake-dreamed about this sort of thing. But also being a techie I have never really come up with a solution that I

Being a very light sleeper myself I have often wake-dreamed about this sort of thing. But also being a techie I have never really come up with a solution that I'd call satisfactory in terms of privacy, surveillance, and potential for abuse by law enforcement. The only exception being a system very much like described in the article: volume meter, coupled to camera. Doesn't record actual audio, serves as entry point for further investigation. But that still puts in place a surveillance infrastructure & associated processes. Which is why, once I've gone back to sleep, and woken up more or less refreshed, I typically go "huh, that needs more thought put in it."