Hardware shut off of iPhone mic (eavesdropping prevention) You may have heard of some news about iPhone (and computer) that some software can eavesdrop on you by, using a software/malware.  A recent example of that is this one: Facebook Doesn’t Listen To Everything You Say, But It Does Listen When You Do This

So I want to prevent anyone from doing that.

For camera, I think a very safe counter measure is to simply block the view of the camera (by a piece of tape, for example).  (Note, by the way, that even the FBI Diretor suggested you to do that.  See this article: FBI Director: Cover up your webcam)

Now how about the microphone?  Perhaps one counter measure is to blocking the internal mic also by a tape.  But I am also thinking whether I should do the following instead?  Plug in a dummy plug into the headset/mic jack (the plug has four rings and does not really connect to a real headset/mic electrically).  Would this disable the internal mic by hardware?  I think this method may be better because I am not sure a paper tape can block the audio completely for the internal mic.  Do you agree with this assertion?

Any suggestion?  Thanks!

The answer may be same or different for iPhones and computers (and other smartphones).  But let's assume for now my main concern for now is iPhone.

Note: I have read this post but I still don't know the answer.  My question is what if the dummy plug has four rings but those rings are not electrically connected to a microphone.
Is your iPhone jailbroken? If not, I am not aware of a single instance where an iPhone that is not jailbroken has been compromised in terms of its camera or microphone. 

The article you link to is about a laptop webcam, and this is a known risk and there are many examples of people's laptops being compromised (especially Windows models).

Assuming your iPhone is not jailbroken, then any apps that are designed to use your microphone need to request access to the microphone. If you do not give permission, then iOS does not allow them to use the microphone. You can also check these settings manually at any time by going to Settings > Privacy > Microphone.

In terms of what you're actually trying to do, this will not work without some sort of software modification. The reason is that the internal microphone is available unless you have attached a microphone (or headphones that also incorporate a microphone). If what you connect to the headphone socket does not contain a microphone, then the internal microphone is still available.