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Background: With microphones being embedded in all sorts of consumer electronics, there is widespread concern that certain actors (e.g. device manufacturers, ecosystem providers, third-party apps) might exploit them to stealthily eavesdrop on users’ private conversations. Several scandals involving smart TVs, smart speakers and even connected toys have shown that these concerns are not completely unfounded.

Similar concerns have been raised about smartphones (see, for example, link1, link2, or link3). Therefore, I’m trying to find out how much transparency modern smartphones provide in that regard.

Question: In Android and iOS, after microphone access permission was granted by the user, is there always some visual indication on the screen while audio is being recorded by ...

  1. third-party apps running in foreground
  2. third-party apps running in background
  3. system apps

If not, are there any notable counterexamples?

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    On iOS, in most situations the status bar turns red. I'm not sure if this happens 100% of the time, however. Feb 24 '19 at 17:52
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    Hard question to answer since it covers all smartphones at every layer. I think it boils down to trust. I don’t trust major players either, although in my opinion IOS offers the most locked down environment, so long as you are willing to trust Apple themselves. As for me, my next phone will be the Librem 5. It may have some issues since this is their first phone, but they do have great experience with supply chain security, offering a security centric transparent platform. I’m willing to sacrifice some experience and convenience for trust. puri.sm/products/librem-5
    – sadtank
    Feb 24 '19 at 19:12
  • Another consideration: my understanding of wiretap law is that users must be informed and consent to recording. Companies doing business in the US are liable, should they be found doing otherwise. So, read the fine print in the TOU, and also documentation regarding sending debugging info to companies.
    – sadtank
    Feb 24 '19 at 19:20
  • I don't think wiretapping is the case here. The user buys a device that is supposed to have a microphone. Then they install applications that are supposed to use the microphone. Then the user allows or disallows applications to use the microphone. The rest is just differences between recording and storing data vs. listening to be able to react to voice commands (example - google voice or Alexa).
    – HackneyB
    Feb 24 '19 at 23:11
  • Come to think of it, if I can turn off the screen, and voice, I should also be able to (easily) turn off the microphone. But that doesn't seem to be a readily used function of smart phones.
    – HackneyB
    Feb 24 '19 at 23:17
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It's best practice to show when a device or application is actively listening, but it's by no means guaranteed. There's a lot of debate about which apps may or may not be listening - Facebook and Instagram, for example, come up a lot - but at the end of the day, clandestine recording is just that: clandestine. So, it's hard to know what's happening for sure.

By the way, I think this question might be a duplicate of another recent one. :)

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  • Can you give examples when an application shows that it is actively listening vs. not listening? I may not be aware of any - just curious. Also I think clandestine recording (that is the subjective case of recording when I don't think the app should be recording vs. when I want it to record) is not necessarily the issue but more the lack of some sort of a "privacy" setting when you just know nothing is listening .. foreground apps or background apps.
    – HackneyB
    Feb 24 '19 at 23:14
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    Well, in terms of the privacy setting, the OS's permissions control is really supposed to be designed to be that. If something has microphone access, users can assume it's always listening; if it doesn't, they're not supposed to. I understand you mean something a little different, but that's one thing to think about. To the idea of a specific app, iMessage is a good one: according to its UI, it's only listening when you're recording a voice memo or dictating a message. Otherwise, it doesn't know anything about what you're saying. Who knows if that's how it actually works though. ;) Feb 24 '19 at 23:36
  • @securityOrange: yep, the "duplicate question" you mentioned was also posted by me, from a friend's account ;) I then decided to sign up myself since I certainly will have more questions along this line in the near future. Although similar, the other question is not a real duplicate. It was focused on data processing and transfer while this question here is about data collection. Just wanted to clarify that. Thank you very much for sharing your helpful ideas!
    – ayon
    Feb 25 '19 at 0:45
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    Got it! You have a nice friend :D That makes sense too, they're not completely identical by any means. Anyways, I like this line of questioning a lot - it's valuable and let's be honest, critically important, to consider as the world fights tooth and nail for its privacy rights in the age of information. Is there anything else you were thinking about? Feb 25 '19 at 1:07
  • Hehe :) I totally agree. More questions on other topics to follow very soon! Right now, I'm trying to find out as much as I can about smartphone-based eavesdropping attacks: Is it technically possible (for malicious third-party apps and/or system services)? Are there reliable ways to detect it, or do users always have to rely on their trust? What could be changed (on a technical or legal level) to achieve more transparency and more robust privacy protection in this area? And so on ... I'm glad that you and others seem to be as curious about this as I am!
    – ayon
    Feb 25 '19 at 1:32
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Android
I found that, beginning with its latest release (version 9 Pie), Android "will restrict access to your phone's microphone, camera, or other sensors when an app is idle or running in the background. (If an app does need to access a sensor, it will show a persistent notification on your phone)" (source).

iOS
iOS has already implemented similar measures years ago: The status bar turns red when an app is recording in the background, and there seems to be no way for app developers to circumvent this (source).

So much for third-party apps running in the background. Remains the question whether foreground apps and system apps can record audio without any visible indication. If you have any insights on this, please share them with us.

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  • Google Assistant will be constantly listening for Ok Google trigger keyword, and that application is always in the background without any change in the UI Feb 25 '19 at 10:32
  • I would suggest the same applies to Hey, Siri, for the record... Feb 25 '19 at 10:33
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    Both services promise to only use what is recorded after the corresponding trigger word, right? And in these situations, there always is a visual indication in the UI. (Although we can't be sure, of course, if the data collected while "listening for the trigger word" is not used in some other dodgy way...)
    – ayon
    Feb 25 '19 at 14:55
  • That is exactly the point. Worse, you may opt in for your provider to collect anonymous samples to improve the recognition of the trigger word Feb 25 '19 at 17:20

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