But there’s still a security flaw in this method. If somebody from Amazon will decide to record you, they just send a reboot command to Echo. After reboot mic’s state will be changed back to normal I.e. powered.
Otherwise, all this hardware protection is moot (mute? ;), because you can listen for a few seconds, and then turn the mute light back on.
Or you can even toggle them back and forth really quick, and turn the light half on and keep the microphone's power pin capacitor charged.
Is there any reason to believe that there's no processing or recording going on?
Doesn’t even need to be at Amazon’s factory in China of where ever. But that is largely feasible too.
The difficulty is more about data exfiltration. Has to be appended to some real ‘normal’ request the next time a legitimate use of the mic is made, then piggybacks uploads on that connection.
Recording all times when a voice is heard would also massively increase the payload sent to the server. If you were just passively network monitoring it could stick out. Which is not something nation states want.
Forget these smart home mics, if I was a nation state I’d just stick with the mobile phones and laptops every person uses.
People are already paranoid about their Alexas inherently (and far more likely to potentially care to look) making them a poor target for hacking. It’s far more useful to turn the thing they carry around with them 24/7 into an active microphone with GPS, and plenty of more exfiltration possibilities with any mobile and desktop OS network traffic.
First, this generally means that when depowered, the output signal line is connected to ground by the ESD protection path.
Second, the actual mechanism which picks up the audio is generally variably capacitive-- a few picofarads-- in MEMS mics, and requires a pretty high bias (~15-200V) voltage to induce a usable signal for the in-package amplifier to be able to pick up the audio.
To not only have the in-package amplifier turned off, but also no significant bias voltage across the microphone electrodes, and somehow pick this up on the other side of the trace would be somewhat miraculous.
I have wireless headphones that work like this and it's a terrible design. If they go out of range temporarily, they unmute. It makes the 'hardware' mute functionality absolutely useless since it cannot be relied upon to stay muted.
This is a long solved problem, a lever switch. Laptops (usually enterprise laptops) sometimes have them to turn on/off wireless communication.
https://ux.stackexchange.com/questions/34956/who-needs-an-ex...