Is my phone listening to me?

Dan was at Sam's barbecue. Sam had a shiny new pizza oven, and Dan said what anyone would say: “Nice pizza oven.”

The next morning, his phone is full of pizza ovens. Pizza oven ads in his social feed. Pizza oven ads on the news site. Pizza ovens everywhere.

“I said ‘pizza oven’ once,” says Dan. “It's listening!”

It's one of the most common suspicions about phones, and it's easy to see why. Liz, naturally, had already gone down a rabbit hole on it.

Researchers went looking

In 2018, researchers at Northeastern University and UC Santa Barbara set out to test exactly Dan's theory. They ran 17,260 popular Android apps through an automated test, watching for any app that switched on the microphone and sent audio off the phone without being asked.

They didn't catch any.

What they did find was plenty of other tracking. Some apps were sending screenshots and recordings of what was happening on the screen to other companies. One of the researchers pointed out that this kind of tracking can paint just as complete a picture of you as listening would.

That's why the careful way to put it is: they didn't catch any app secretly listening. Their test had limits. It only covered Android, it ran automatically without logging in to apps, and it couldn't rule out every possible trick. Nobody can honestly promise that no phone has ever listened. But the evidence doesn't point that way, and there are simpler explanations.

The little dot

There's also a check you can do yourself. On current phones, when an app is using the microphone, a small dot appears at the top of the screen. On an iPhone it's orange (or green, if the camera's on too). Android phones show a similar indicator.

Dan checked. No dot.

“Then how did it know?”

Three ordinary explanations

Liz's answer comes in three parts.

1. What you look at. “Did you look one up afterwards?” Dan had. Only to check the price. Apps and websites routinely tell advertising companies what you look at. It's like a shop clerk who follows you out of the store and into the next one, telling every salesperson what you were browsing.

2. Where your phone has been. Your phone knows where it's been, and many apps share location with advertisers. Dan's phone spent the afternoon at Sam's house.

3. Whose Wi-Fi it joined. Dan's phone was on Sam's Wi-Fi. To ad companies, phones on the same home Wi-Fi can look like one household, because they share the same internet address. And Sam had been shopping for pizza ovens for weeks.

“So Sam's searches became my ads?”

“Probably,” says Liz. Nobody outside the ad companies can say for sure which route it was. But each one is real, documented, and doesn't need a microphone.

What the video left out

Voice assistants are a different story. Siri, Alexa and Google Assistant do listen, on purpose, for their wake word, and they sometimes wake up by mistake. That's a separate subject from apps secretly listening for ads, and nothing here says assistants never hear you.

Coincidence plays a part too. You see a lot of ads and forget most of them. The one that matches something you said is the one you remember.

Dan's conclusion: it wasn't listening. It was following his shopping. And Sam's.

So creepy ads usually don't need a microphone. Tracking, location, and who you know explain most of them.

What you can do

• Turn off ad tracking (the advertising ID is a code that lets ad companies recognize your phone): on iPhone, Settings → Privacy & Security → Tracking, then turn off “Allow Apps to Request to Track”; on Android, delete your advertising ID under Settings → Privacy → Ads (menu names vary by phone).
• Check which apps can use your microphone: on iPhone, Settings → Privacy & Security → Microphone; on Android, Settings → Security & privacy → Privacy → Permission manager → Microphone. Switch off the ones that don't need it.
• Watch for the dot at the top of the screen. If it shows up when you're not using an app that needs the microphone, find out which app it is.
• Expect fewer creepy ads, not none: other tracking carries on.