An OTA firmware update can change this behavior overnight. Unless it's a physical bounce switch that actually disconnects power mechanically, you are still at the mercy of someone else.
As far as I understood from the schematic [0], the power line of the mic is directly connected to the LED.
Looks like when you press the mute button, you both light the led up and pull-up the transistor gate (It looks like PNP so, it turns off when you apply power to the gate). This effectively cuts off power from the mic itself.
So, the LED is not controlled by firmware but, by the behavior of the circuit.
AFAIK, OTA updates cannot re-wire PCBs or do we have nanobots now?
> Unless it's a physical bounce switch that actually disconnects power mechanically
That's literally what you're looking at.
The schmitt-trigger and the DFFs debounce the switch in hardware, and then the FET that controls the power input to the microphone also controls the power input to the LED. What do you want, a relay?
Firmware can only reset the DFFs (which does turn on the microphone), but it can't change the physically coupled LED / mic-power behavior.
Perhaps you could disable the button, but I don't think a firmware update can change the red LED on == microphone off behaviour. This is a good compromise IMO, as if the microphone off button stops working then you can deduce that the firmware may have been tampered with.
As I understand the teardown article, it is impossible for a firmware update or any malicious SOC code to enable the microphone without also turning the red led off.
Not as good as a physical switch I guess, but better than some implementations of laptop webcam activity lights at least...
If the device reboots after remote update, wouldn't that enable the mic? I read that when you power on the device, mic is on by default. So that could be a way to turn on listening without consent.
Looks like when you press the mute button, you both light the led up and pull-up the transistor gate (It looks like PNP so, it turns off when you apply power to the gate). This effectively cuts off power from the mic itself.
So, the LED is not controlled by firmware but, by the behavior of the circuit.
AFAIK, OTA updates cannot re-wire PCBs or do we have nanobots now?
[0]: https://1.bp.blogspot.com/-vVhoXpEtTXo/X_0iLmz9gcI/AAAAAAAAB...