Generally, such devices’ microphone function(s) can be defeated when desired (best is if an external plug [only] can be used to do so, as a mechanical “open” cannot be defeated no matter how much time / effort / money the NSA throws at it from a remote location. If they have a truck outside your house, you have a bigger problem!)
Perhaps some computers are different, but on my machines, either it is not possible to activate the internal mic when the mic jack has a plug in it, or, there is no internal mic in the 1st place.
Of course, if about 20 million people were devious and fed a stream of canned but “suspicious” audio with all the right “keywords” into U.S.’ communications network, at semi-random times, that’d overload NSA’s whole system. The problem is, we (or at least I) actually DO want them listening for real terrorists, so the question is how to limit the surveillance to only that. I have no real answer for that, as we have seen how easily any “legal safeguards” can be avoided or ignored.
On Saturday’s Huckabee there was an electronics type guy who says the police can tap your phone even when it’s turned off.
A month or so back there was a “news” report about microphones and cameras in televisions.
The government can do things we can’t even imagine.