I'm forking this from this question, to which I gave a partial answer.

These folks claim that their hardware includes a physical kill switch for the internal microphone that reversibly interrupts the wire. They provide a reference diagram here.

This raises an interesting possibility for matters of surveillance. Is a reversible switch a workable solution for microphone surveillance exploits?

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    Can you define "reversible"? Do you mean "non-permanent" ie non-destructive? Apr 12 '16 at 20:48
  • "Non-permanent".
    – user107181
    Apr 12 '16 at 20:48
  • This isn't new technology. The ability to use a physical switch to disable features from hardware has been standard for many years. Apr 12 '16 at 21:21
  • I'm very confused by the question. Is it possible? Of course, it's called a switch. But are you asking why people don't care more about it? If you are, I'm not sure we can answer that. Also, from another comment, you seem to be primarily concerned with phones. Is that true? If it is, you will need to edit that into your question. I can tell you that it would be weird to add a switch for the mic on a device that that is primarily used for voice communications ....
    – schroeder
    Apr 13 '16 at 0:06
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    @schroeder At least in Europe, people use portable miniature internet-connected computers (commonly called smartphone) for a lot of stuff completely unrelated to voice communication. This is even more true for tablets. But also for dumb phones, I can understand the distrust in firmware causing the wish to make sure the microphone does not work if you are not actively using voice communication. Apr 14 '16 at 6:51

Well, yes, it's called a switch.

Microphones from a hardware perspective are (in the case of electrets, at least) a capacitive component which produces a small current when the membrane moves due to sound. By amplifying this signal you can capture a sound signal.

By simply disconnecting the audio line from the mic itself, or just turning off the amplifier circuitry, you cut the input and no longer provide any audio to the hardware. It's as simple as unplugging a 3.5mm jack from your phone, except with a switch.

  • Thanks the input. How much (relative) space is there for that switch in a phone? I would think that the space would be the primary constraint there.
    – user107181
    Apr 12 '16 at 21:33
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    @Vessik As an after-market mod to a modern smartphone it's difficult. You could do it, probably, with a really low-profile DIP switch and a hole in the case, but it'd be hacky. As an in-built feature it'd be easily doable. But the link you showed was talking about a laptop, so there's plenty of space there.
    – Polynomial
    Apr 12 '16 at 21:44