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by newnewpdro 2787 days ago
> I would love to see a light come on if the camera or microphone is receiving power, and then only turn on power to these devices when a program requests it.

Isn't the microphone a simple passive device no different than a voice coil in a magnetic field? I don't think it's that simple, since it won't be powered.

My understanding is that there's often a reconfigurable circuit in the sound chip which determines where the lines in and out are routed. So even if you've physically disconnected the microphone, but left internal speakers connected, it's possible to turn the speakers into a microphone via software alone.
1 comments
bigiain 2787 days ago
There's at least a pre amp and a d/a converter that the mic needs to have powered up and running before any of it's signal can be used by the rest of the computer.
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newnewpdro 2787 days ago
Which will all be inside an IC, away from the microphone.

So what, does the light turn on whenever the entire IC sees power? Because if it relies on a signal from within the software-controlled IC, that's not exactly trivial to audit.

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XMPPwocky 2787 days ago
The trivial solution would be a LED + resistor just wired across the mic's power rails.
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newnewpdro 2786 days ago
When the microphone is a passive connected to a multifunction IC there's no such power rail.
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justtopost 2786 days ago
Most laptop mics are condenser electret mics which usually use a small dc current, although not always.
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newnewpdro 2786 days ago
Not the last time I went down this road hardening a Thinkpad, see Step 6 at [1] (not my site). I haven't bothered with any smartphones yet, so I can't speak to what they tend to use for a mic. But if I carried one I'd definitely rip out all the voice coils and rely on a pair of headphones w/integrated mic for voice comms to mitigate potential for eavesdropping.

[1] https://blog.patternsinthevoid.net/replacing-a-thinkpad-x60-...

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colejohnson66 2786 days ago
When replacing the lightning assembly on my iPhone 6, I noticed that the microphone looks passive. Here’s a photo[0]; It’s the little bronze(?) square next to the headphone jack.

[0]: https://www.ifixit.com/Store/iPhone/iPhone-6-Lightning-Conne...

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