[lloeki]

Actually I don't think it is listening at all when not in use. In fact the sound card even powers itself down when not in use, which can actually be heard in some cases (with some badly shielded/grounded HP for example). It's on when the prefpane is shown for the purpose of displaying that VU meter but as soon as you quit the prefpane, the hardware turns off. And as soon as an app opens it, it turns back on.

Even then, let's assume the sound card is always on (like my old SB16):

- what would listen to it if it was on? necessarily some code, or else it just goes straight to /dev/null.

- so if it's external code injected by a malicious guy, what prevents him from setting it back to internal (and setting it back to line-in when you're looking)? Or craft all sorts of drivers hooking into or replacing AppleHDA.kext or whatever?

- but if it's not external code it has to be internal (i.e Apple provided), so what would prevent Apple to simply tell you it's off when it would not actually be?

- and since line-in disappeared but the (HDA or whatever) sound chip certainly still has this functionality, what would prevent Apple from having a second microphone plugged into that line-in, completely hidden and uncontrollable?

Now Poe's Law kicks in and I can hear headlines already "Apple removed the line-in on purpose to spy on us!"