These high-pitched signals can be hidden
Many people have experienced situations where they have talked about something with a friend, like needing a new TV and later that day, an ad for that same product appears on their smartphone.
This is called sonic snooping, where adverts for goods and services appear on smartphones soon after a person talks about them or they are discussed on TV.
For years, iPhone and Android users have been convinced that their social media accounts are listening to their conversations, something platforms like Facebook have long denied.
But according to new research from NordVPN, advertisers are listening to smartphone users, not social media apps.
Apparently, ad companies are using a type of data monitoring called ultrasonic cross-device tracking to listen to background noise and provide personalised ads to users.
According to NordVPN, this cross-device tracking method sees apps use ultrasonic ‘audio beacons’ which cannot be heard by the human ear to “link all the devices you own to track your behaviour and location”.
These high-pitched signals can be hidden in TV adverts or online videos.
Once a device’s microphone picks them up, it gives advertisers the ability to identify what the user has just been watching or talking about.
Different apps can listen for these beacons to keep an eye on what you have been doing.
This is why some apps ask you for permission to access your microphone.
The impact of this tracking method is seemingly widespread.
NordVPN conducted a survey on more than 1,000 people in the UK.
It found that 45% of Brits claim to have seen an ad for something appear on their phones soon after talking about it or watching it on TV, without ever searching for it online themselves.
Half of the survey respondents said this made them as though they were being followed.
Sixty-two per cent said they had no idea how to prevent this while 12.5% said the adverts “scared” them.
While it is impossible to stop your smart home devices from emitting these ultrasonic waves, there is a way to protect against unwanted tracking.
NordVPN’s Adrianus Warmenhoven said: “While it’s impossible to stop the ultrasonic beacons working, you can reduce the chance of your smartphone listening for them by simply restricting unnecessary permissions you have granted the apps on your device.”
To change the permission that apps have, go to your phone’s settings menu and look for the privacy option.
Here you should be able to see which apps have access to your microphone and limit it where necessary.
Alternatively, you can use a secure browser or get a VPN, which encrypts all of your online activity.