Many apps on your mobile phone have the ability to listen to your private conversations so you can deliver personalized ads, according to experts at NordVPN, which specializes in creating virtual private networks.

Who hasn't been upset to see an ad on social media for a particular product, shortly after talking to friends or family about the same product?

According to NordVPN's new research, mobile apps are able to use microphones to monitor our own dialogues using intelligent technology based on ultrasonic tracking.

Through this technology, our phones can often capture conversations that occur in the background, only to be used later by apps to deliver personalized ads.

NordVPN also warned that the cross-device tracking method could also include apps that use ultrasonic "sound signals" that the human ear cannot hear.

Some apps monitor us with microphones with intelligent tracking technology via ultrasonic devices (Shutterstock)

In one blog, they explained, "For example, you might watch TV when an advertisement for toothpaste appears. Unbeknownst to you, the TV ad has built-in ultrasonic signals. While the ad is playing, your phone's microphone listens for signals (if it has sufficient permissions). You pick up the phone, go to social media and see the same ad you just saw on TV. Shell? No, it's just very advanced and elaborate marketing."

NordVPN recently conducted a survey that found that cross-device tracking involving ultrasonic signals is a widespread problem, with 45% of UK respondents saying they noticed ads after talking about or hearing about a product on TV.

Interestingly, 12% of Americans surveyed indicated that they felt "privacy was important" after seeing these targeted ads, and 20% said they were happy to receive such accurate ads.

Fortunately, there are ways you can restrict your device's access to prevent such ads, and NordVPN has advised the following steps to reduce cross-device tracking:

  • Review app permissions: You can restrict your device's eavesdropping permissions, by going to App permissions in Settings and restricting apps that you feel don't require microphone access.
  • Read privacy policies carefully: Although tempting to skip them, reviewing the app's privacy policy can protect you from "eavesdropping" on your phone, so check if it indicates your phone's microphone and for what purpose it will be used.
  • VPN use: Using VPNs to secure your internet browsing through encryption, hiding your computer (IP) address, and hiding your activity from your ISP, governments, and other third parties.