The important part that everyone seems to be ignoring is Kyllo v United States[1]. When new technology is involved, the 4th Amendment's protections against searches is present if and only if the technology "is not in general public use"[2]. If a technology becomes common and familiar to the public, a warrant is no longer needed to use it to see "details of a private home that would previously have been unknowable without physical intrusion"[3]

The details of how your internet microphone works doesn't matter, because it's not thoe microphone that you should be worrying about. If these devices are in "general public use", you no longer have an expectation of privacy from the technology itself (not any particular product). The police in Kyllo v United States brought their own infrared camera.

[1] https://en.wikipedia.org/wiki/Kyllo_v._United_States

[2] http://caselaw.findlaw.com/us-supreme-court/533/27.html

[3] Ibid.