For digital microphones it can also be very simple. Consider a PDM microphone, if you disconnect the data line and have it stick to either high or low through a pull-up, the signal becomes DC. This wouldn't be pop-free by itself, but it should be rather easy to make it so through DSP.

(FWIW, you can also easily mute pro-audio microphones by shorting (+) and (-) together. The attenuation is determined by the output impedance of the microphone, usually a few hundred Ohms, divided by the resistance of your switch. Typically you'll get like 60 dB from this, which is perfectly fine for muting in a normal setup, but if you crank the preamp all the way up you can still get a usable, albeit very noisy, signal out of it.)

Just send the mic signal through an op-amp with an enable input.

This is how the Google Home Mini does it. When you flip the mute switch, an AND gate kills the digital signal from both microphones (a stereo microphone pair share a single data line). All the audio hardware gets is a string of 0 bits at that point.

I'd like to see that too, but I don't think we will. I suspect it's a magnetic switch and I'm also curious which lines it cuts.

FWIW, you can still get some audio from an accelerometer if you can get it to report data with a high enough frequency.

Not sure what you mean about iPhones, their information does not mention the iPhone (and I would not expect it to).

I meant iPads but got confused. Thanks for pointing it out.

Ingedients being hard to come by, and the market uninformed but spend-happy, hucksters appeared and the "medicine show‘ emerged. Patent medicines were also amongst the first widely advertised products in mass media beginning in the mid-19th century.

https://www.collectorsweekly.com/articles/how-snake-oil-got-...

http://gen.lib.rus.ec/scimag/?q=10.1007%2Fs12686-014-0200-1

http://www.npr.org/blogs/codeswitch/2013/08/26/215761377/a-h...

http://umm.edu/health/medical/altmed/supplement/omega3-fatty...

https://archive.org/details/applerefjan78/

Circuit diagrams, bank switched memory details, pretty sure someone dedicated could have built themselves their own machine with access to the manual and the right rom dump and system floppy disks...

I don't see why you assert that is has to be electro-magnetic based, as long as the gating is down by a 'dumb' fixed transistor rather than a programmable chip, then it's a hardware disconnect.

I hope you're right, and I'd agree that would qualify as a "hardware disconnect". It's a little confusing given the mention of the T2 chip; they do differentiate some specific models which are "hardware alone", and at least imply that the T2 chip does not flip the off-switch on those. I'll have to go dig into iFixit's tear-downs to see if they found anything. For the 2020 iPad, they specifically mention "MFI compliant cases", so we can be fairly certain that one's done with magnets.

It's the same sensor that's used to detect if the lid is open in general. Triggering it will prevent the display from turning on, and will make the computer go to sleep if it isn't running in "clamshell mode" (running on AC power with an external display attached).

Why is that? Any case, including not "MFI", could put a magnet at the location if that was the case. Doesn't "MFI" mean that they make it only work with cases that are identified via the software to have paid their certification to Apple?

Also, why would detecting a closed iPad sleeve require "electro-magnet based communication"? Seems like detecting presence of a magnet would be enough.

We have automatic steam cutoffs that are entirely mechanical. I have built a state machine out of hardware logic that would have cost less than a dollar with a microprocessor but was preferred because it could be verified to work and not be remotely “upgradeable”.

You can do the whole thing in analog fairly easily. The hardest part would be to get the magnetic sensor integrated into the same chip, but I guess that’s been a solved problem for a while.