I have vague memories of iPod Linux (or Rockbox, I can’t remember) having a feature where you could record voice notes using your regular headphones using the same technique
I recall when I was a kid decades ago, being able to plug a speaker directly into the microphone jack and use it as a microphone, without any modifications whatsoever.
We could do the reverse too, plug a microphone into the speaker jack and hear sounds coming out from it.
Not sure if it's mentioned in the article but microphones can be speakers too...
Only dynamic mics, which are relatively rare and seldom encountered without an attached preamp. The vast majority of mics for PCs are condensers and electrets.
Anything can be a speaker, briefly and only once, if you apply enough voltage to it...
Not all speakers work well as dynamic mics; and in fact turning on mic mode may enable the bias voltage, which could either burn out the voice coil or hold the diaphragm against the stop, making it even less likely to pick up any sound.
Jack retasking, although documented in applicable technical specifications, is not well-known, as was mentioned by the Linux audio developer
This could be a "bubble effect"; the Realtek codecs mentioned have a Windows utility to configure the jacks, which countless otherwise non-technical users would've seen and interacted with, so awareness of this feature is probably higher than they think. Fun fact: the "ALC" prefix in their codec names stands for Avance Logic, which was acquired by Realtek and they just kept that prefix well into the HD Audio era.
I hadn't thought about whether this would still with modern speakers, but this was the common assumption for several older types of speakers and microphones.
One of the first "science experiments" my dad showed me was the other direction: Dismantling our telephone and demonstrating that the carbon microphone (yes, I'm old) in the handset would also work as a (really bad) speaker.
It's pretty unlikely that Meta is actually eavesdropping on your conversations, because it'd be immediately obvious from battery usage. The ability to turn speakers into microphones doesn't help if the speakers aren't actually connected to an ADC, and both of the modern smartphone OSes limit you to on the order of hundreds of samples per second, so it's rather difficult to get anything sensible without either doing a bunch of local analysis or exfiltrating it, both of which would be visible.
It can be done with neural networks [1]. Also, speech doesn’t need much bandwidth to be intelligible. You would need control of the analog filter between the accelerometer and the ADC. With 250/s acceleration samples you can reconstruct a signal of a bandwidth of more than 100 Hz anywhere in the spectrum. That is called undersampling.
Not sure if it's mentioned in the article but microphones can be speakers too...
We could do the reverse too, plug a microphone into the speaker jack and hear sounds coming out from it.
Only dynamic mics, which are relatively rare and seldom encountered without an attached preamp. The vast majority of mics for PCs are condensers and electrets.
Anything can be a speaker, briefly and only once, if you apply enough voltage to it...
But you probsbly think about smaller form mics like found on headsets (Electrets).
I hear what you did there
Jack retasking, although documented in applicable technical specifications, is not well-known, as was mentioned by the Linux audio developer
This could be a "bubble effect"; the Realtek codecs mentioned have a Windows utility to configure the jacks, which countless otherwise non-technical users would've seen and interacted with, so awareness of this feature is probably higher than they think. Fun fact: the "ALC" prefix in their codec names stands for Avance Logic, which was acquired by Realtek and they just kept that prefix well into the HD Audio era.
One of the first "science experiments" my dad showed me was the other direction: Dismantling our telephone and demonstrating that the carbon microphone (yes, I'm old) in the handset would also work as a (really bad) speaker.
[1] https://dl.acm.org/doi/abs/10.1145/3478102