Zahid Hossain, a private-sector employee in Dhaka, decided during a heatwave that he would buy an air conditioner on instalments. He told nobody, not even his family. He opened Facebook to look up prices and found his feed already full of AC advertisements, complete with EMI offers. The question he asked is the one everyone asks eventually: how did Facebook know?
Not the microphone
The popular theory is that the app secretly listens through the phone's microphone. Facebook has always denied it, and independent tests by security researchers have never found the app recording audio; doing so would also drain the battery and show up in the network traffic that thousands of engineers watch. The truth is less dramatic and, in a way, worse: Facebook does not need to listen, because you told it in other ways.
How it actually works
- What you do on Facebook. Every post you pause on, like, comment on or share, in Facebook, Instagram and Messenger, feeds an interest profile. Pausing on a friend's photo of a new AC counts.
- What you do off Facebook. Most shopping websites and many apps carry the Meta Pixel or SDK, a piece of code that reports your visit back to Facebook. Search "AC price" on a Bangladeshi retailer's site and Facebook knows within seconds. In your settings this is called Off-Facebook Activity, and the list is usually long.
- Your phone's advertising ID. Android and iOS give every phone an ID that apps share with ad networks, so a search in a shopping app can be matched to your Facebook account.
- People like you. Even with no direct signal, Facebook infers: a man in Dhaka, aged 35, salaried, in May, whose friends have been looking at ACs, gets AC ads. This is "lookalike" targeting, and it is what makes the ads feel telepathic.
Zahid almost certainly visited a retailer's website or tapped an AC ad in passing; the cache of several hundred megabytes that the Facebook app quietly accumulates is a sign of how much it fetches and tracks even when you are not looking.
How to cut it off
- Facebook app: Settings, Your information, Off-Facebook Activity. Clear the history and turn off future activity.
- Settings, Ads: switch off "ads based on data from partners" and review the interest categories.
- iPhone: when an app asks to track you, choose Ask App Not to Track. Android: Settings, Privacy, Ads, delete or reset the advertising ID.
- Use a browser with tracker blocking for shopping, and log out of Facebook in that browser.
None of this stops ads; it makes them dumber. For some people that is exactly the goal.
