Your Video Conferencing App May Listen, Even When Muted

Watch what you’re saying

  • A new research paper finds that common video chat apps don’t mute the mic when they say they do. 
  • At least one app sends audio statistics while the mic is supposedly muted. 
  • The best way to stay safe is to disable the microphone yourself.
Someone's face on a screen via video conference in a conference room with people.

Christina @ wointechchat . com

A new research paper finds that video conferencing apps listen via the mic even when they appear to be muted. Other participants cannot hear you, but your audio is still sent to the server.

Muting your audio in a video conference call is good practice. Nobody wants to hear the trash truck outside your window or the washing machine hitting its spin cycle. But we also use muting to let us have a private aside with somebody right there in the room with us, and we might expect that mute means mute, and that no audio is leaving the computer. But it turns out that our private conversations might get a lot further along before being silenced. The good news is that there’s an easy fix. 

"For the most part, users have accepted these apps in their personal space without much thought about the permission models that govern the use of their private data during meetings," writes Kassem Fawaz, assistant professor at the University of Wisconsin, in a research paper. "While access to a device’s video camera is carefully controlled, little has been done to ensure the same level of privacy for accessing the microphone."

Mic Drop

The problem is that the microphone never gets muted. That is, the mic doesn’t get muted at the input stage. Instead, the audio feeds into your video conferencing app or the website via your browser, and the mute is enacted at that level.

In some ways, it makes no difference—other meeting participants won’t be able to hear your audio, regardless. But in others, it makes all the difference. If your audio is leaving your computer, it can be (and is) accessed by the videoconferencing service and could theoretically be included in audio recording and transcripts of the video meeting. 

While access to a device’s video camera is carefully controlled, little has been done to ensure the same level of privacy for accessing the microphone.

For example, according to the research paper published by Fawaz, Zoom alerts users if they try to speak with the microphone muted, which indicates that the software is listening even while you thought it was not. 

This audio could also be used to identify what you are doing. For instance, analysis software could recognize car noise, kitchen sounds, or other scenes and, from there, infer your current activity. 

But mostly, the problem is trust. In Fawaz’s research, respondents overwhelmingly assumed that mute meant mute, that their audio had been cut. 

"I am sure that it is disclosed somewhere in the terms and conditions, but seeing as the vast majority of people don’t read those thoroughly, that doesn’t do much to make users aware," security writer Kristen Bolig told Lifewire via email. "I think companies need to be a little more transparent and upfront about these things."

Mute Switch

As ever, it falls to the user to protect themselves. The easiest way is to use a hardware mute switch, but this only works when you use an external microphone. There are purpose-built mute switches on the market, some of which have a silent mechanism, so the switch itself will not be annoying, but if you’re using a mic and an audio interface, you can easily mute the input at the mixer/audio interface level. 

A condenser mic reflecting a pink light.

Sandra Tensdchert / Unsplash

If you’re using a laptop’s built-in microphone, you can’t use a hardware cut-off. Apple’s computers—the Mac, iPad, and iPhone—have a deservedly-good privacy reputation, but even they cannot disable the mic easily. While the video camera input can be switched on or off in the Control Center panel, there’s no quick toggle for the mic. 

In the case of the Mac, you can visit the System Preferences panel for sound and drag the input level slider down to zero. You could leave this panel open during your call, but it’s still a pain.

And some web browsers have the option to disable microphone access for the current website, which is also a fiddly workaround, but handy for when you’re conferencing via a web app. 

Platform vendors could make this easier. iOS and macOS already show an orange dot in the menu bar to indicate that an app is using the mic, but it’s not interactive. What we need is a system-wide, 100% trustworthy way to quickly mute all mic input. Then, it wouldn’t matter that the videoconferencing apps ignore our privacy.

Until then, you’d be wise just to watch what you say.

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