I searched for a coffee maker on my laptop. Ten minutes later, my phone showed me ads for coffee makers on three different apps. Same brand. Same model. My wife had not searched for anything — but her phone started showing the same ads because our devices were on the same Wi-Fi network.

That was the moment I dug into privacy settings. There is one setting in particular that cuts off the data pipeline that feeds ad tracking across apps, and it takes about thirty seconds to enable on either iPhone or Android.

On iPhone: Ask App Not to Track

Go to Settings > Privacy & Security > Tracking. You will see a list of apps that have requested permission to track you across other apps and websites. Toggle off “Allow Apps to Request to Track.” This sets the default to “no” for every app — they cannot even ask.

If you leave the toggle on but deny each request individually, apps still collect data through other means. The blanket off switch is the strongest protection. Apps that respect the setting stop using your device’s advertising identifier, which is the unique number advertisers use to build a profile of your behavior across different apps.

On Android: Delete your advertising ID

Go to Settings > Privacy > Ads (the exact path varies by phone manufacturer). You will see an option to “Delete advertising ID.” Tap it. Your phone generates a new, blank identifier. You can also toggle off ad personalization entirely so apps do not use your data to target ads.

Android does not have the same per-app tracking permission model as iPhone, so deleting the advertising ID and disabling personalization are your two strongest controls. Do both.

The cross-site tracking setting you missed

On iPhone, go to Settings > Safari and scroll down to “Prevent Cross-Site Tracking.” Make sure it is on. This stops websites from following you from one site to another — the mechanism behind those ads that follow you around the internet. On Android, Chrome has a “Do Not Track” setting in Privacy and Security, though it is weaker because websites are not required to honor it.

What changing these settings actually does

Your phone still collects data. Apps you use can still see what you do inside that app. What changes is that data from one app can no longer be combined with data from another app to build a cross-app profile of you. The coffee maker you searched for in a browser app cannot follow you into social media, weather, and gaming apps.

You will still see ads. They just will not be based on a detailed dossier of your behavior across every app on your phone. The ads become generic — and that is the point.