That's true. Wired devices have the power to listen passively indefinitely and to record as much as they want. As I updated my post to mention, Google apparentl

That's true. Wired devices have the power to listen passively indefinitely and to record as much as they want. As I updated my post to mention, Google apparently added Google Voice search to Chrome at one point. With wired devices, I've comforted myself with the analysis that users could detect subterfuge by looking for unexpected network traffic. A device can't record my voice and transmit it centrally all the time without generating noticeable network usage. It could, however, record for a while and send in a burst later, perhaps concealed within other traffic like a weekly software update. Nevertheless, I think a close examination could detect foul play. I do wonder whether phones could conduct the same type of subterfuge: Perhaps there ought to be a "phone surveillance challenge" that's kind of like the Underhanded C contest. Each year, contestants submit a phone app that runs in the background on a phone over a 48 hour contest period simulating normal usage. At several points during that period, an important conversation will be overheard. The app that does the best job recording the conversations and remaining undetected is the winner. Naively recording all audio and storing it will probably drain the battery. It also needs to be compressed, though bit rates as low as 5 Kbps seem to be intelligible. If we record at 5 Kbps, then it will require only 108 megabytes to store 48 hours worth of audio. The compression might eat up CPU, however. Perhaps skilled contestants will find a way to do it cheaply. If we're a smart contestant, we don't indiscriminately record and store all audio. Instead, we want our contest entry to record the human conversations. I'd hazard a guess that our highly skilled contestants can come up with cheap passive methods of detecting human voice, comparable to the ones that listen for "Ok Google". So our contest entry only wakes up when it hears human speech. Our contest entry won't transmit anything over the airwaves regularly, since that uses battery. However, we know the phone will be charged at least once in 48 hours. We'll wait until it's charging to upload our recordings. Even better, we'll time our transmission burst to be right after some other network activity, like a daily software update. Or if the phone is plugged into a computer, we can compromise it as well and extract data that way. Sounds like a fun contest.