25

I recently got my hands on an Echo Dot.
I'm hesitating to install it, since I'm concerned about my privacy. According to Amazon's privacy notice, they may use all data they capture.

I've noticed that the Amazon Echo comes with a mic mute button, which would be perfect for cutting down on voice data. But since Alexa is closed-source, I wouldn't be convinced that this button will keep my mic off under all circumstances.

Is the Echo mic mute button a software or hardware kill switch?

My searches didn't turn out much, mainly because the web is filled with low-quality news and non-technical articles.

18

According to Jeff Bezos, it's a hardware button, and various sources seem to agree from the teardowns

A forum post at the EEVblog forums quotes a video featuring Jeff Bezos, the founder of Amazon:

In this video about Jeff Bezos being interviewed by Walter Isaacson at around the 6 min mark, Bezos claims the mute button on the Amazon Echo is physically connected to the mic amplification circuit, making it impossible to enable again via software.

This is also supported by a reddit thread in which it is said that "Basically it is a physical analog connection that cuts off circuit flow to the mic." Another commenter added:

No voltage to mics when mute is on. You're correct as well about the state of mute being software controllable. That said, the state of the LED under the button is tied electrically to if the mics are on (same circuit), so there's no possible way the mics can be powered without you knowing it.

That said, those sources aren't particularly clear on which models they're referring to. Taking a further look at the teardown linked in the forum post may be interesting to verify this.

Another source that supports the 'hardware button' theory is the Apple Insider site, which discusses a previous Echo vulnerability. It notes that:

Despite gaining access to the "always-on" microphone, the hack cannot get around the physical mute button on the device, which disables the microphone completely. This switch is a hardware mechanism that cannot be altered with software, though it is feasible that with extra work this button could be physically disabled by a determined attacker.

Disappointingly, the iFixit teardown doesn't include a good image or any commentary on the mute button circuitry for the proper Echo device. Even so, there's a substantial amount of evidence that it may be a hardware button after all.

  • Just to clarify: From what I'm reading in your post it sounds like it actually is a software button, but it is physically tied to the light? I think this would explain why the Echo can still talk (per my answer), but it does give you a safe indication whether the mic is on or off. – anonymous2 Dec 12 '17 at 15:42
  • @anonymous2 I don't believe so; the quote says that the mic and light are on the same circuit and it is explicitly said that the circuit is broken to the microphones. I'll take a further look to see if I can verify what's being said though and clear it up a little more. – Aurora0001 Dec 12 '17 at 15:57
  • Would it be possible to find out if the Echo has the hardware to use the speaker as a microphone? – Andrew Morton Dec 12 '17 at 18:28
5

The button feels like a momentary push switch and I'm 99% certain that the mute state is reset on a reboot.

With both of these in mind I would suggest that it's a software controlled mute rather than physically disconnecting the mic.

  • This source claims that the switch does persist reboots: Read the section 'Disabling Your Echo's Microphone'. Though they don't use the Dot, I'd assume the two devices behave the same. – FMaz Dec 12 '17 at 12:20
  • ok, I'm not at home to test mine just now, so possibly. I would still say the way the switch feels to be a momentary push that it's all software – hardillb Dec 12 '17 at 12:21
  • You're right, it does feel like a software button. There are hardware boards (and hence hardware kill switches) that support this button type too, though. For the sake of correctness, I'll wait and see if someone can give me a more technical explanation. Otherwise, I'll probably just rip it apart and try to check it myself. – FMaz Dec 12 '17 at 12:26
  • Just because it is momentary does not mean it is not hardware. Hardware latches can be used to store data. For example the latch stores that it is muted. This signal then cuts the Mic connection. The same signal could be used by software as an input to control the light. – Eric Johnson Dec 12 '17 at 17:58
3

I agree with @hardillb's assessment: it's a software button. I have several basic reasons for believing so:

  1. The mute button turns on a red ring light. While it would be possible to do this with a hardware button, it makes more sense logistically to do this with a software button.

  2. If I'm not mistaken, the mute button controls the speakers as well as the microphone. According to this source, when you turn on the Alexa, it goes through the normal boot sequence and says, "Hello!" before it returns itself to the muted state. If it were a hardware button, I would expect it to be unable to say anything.

  • 2
    It can be both though: a hardware button for the mic and a software button for the speaker: The speakers could simply check the state of the microphone hardware button via software. – kapex Dec 12 '17 at 17:25
  • No, the mute button doesn't turn off the speakers. (source) – BraveNewCurrency Dec 19 '17 at 6:32

protected by Helmar Jan 1 '18 at 13:20

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