What an advertising ID is
An advertising identifier is a long string of letters and numbers that your phone’s operating system creates for advertising and measurement. Apps can read it, and so can the advertising companies whose code runs inside those apps. It is not your name, phone number or email address. Its purpose is to be a consistent label for your device.
The idea behind it was to offer something more controllable than older, permanent device identifiers. Because you can reset this one or switch it off, the system gives you some say in how long a label stays attached to you. Both major platforms offer a version of it, although the names and menus differ and have changed over the years.
How it gets used
Suppose you use two different apps that both contain the same advertising software. Each app can tell that software, “this device, with this identifier, did something.” The ad company can then connect the two sets of activity under one label, even though neither app knows what you did in the other.
Typical uses include:
- Ad personalization. Showing ads related to interests inferred from your activity across apps.
- Frequency capping. Avoiding showing you the same ad many times.
- Measurement. Working out whether an ad led someone to install or buy something.
- Fraud detection. Spotting patterns that look like fake installs or automated activity.
Some of these are fairly harmless. Others involve building a detailed profile. Whether you are comfortable with that is a personal call, and it can reasonably differ from app to app.
What it does not do
A few common misunderstandings are worth clearing up.
- Restricting it does not remove ads. You will usually still see ads, but they should be less tailored to your history.
- It is not the only way to be recognized. An account login, an email address, an IP address or details of your device and browser can also help companies connect activity. Turning off the advertising ID reduces one route, not every route.
- It does not control what a single app knows about you. An app can still keep its own records of what you do inside it.
- It does not affect websites in the same way. Browsers rely on cookies and other techniques, which have their own settings.
So treat these controls as a useful layer, not a complete shield.
Reset, restrict or delete
Different options exist, and the terms matter.
Reset. Generates a new identifier. Old profiles built on the previous one no longer match your device, so personalization starts over. This is useful if you want a fresh start but are fine with ads in general. Over time a new profile builds up again, so some people reset periodically.
Limit or opt out of personalization. Tells apps and ad networks that you do not want ads based on your activity. Whether that is enforced technically or relies on companies honoring your request depends on the platform and version.
Delete or remove. On some Android versions, you can delete the advertising ID entirely. Apps that ask for it then receive a blank or zeroed value instead of a usable identifier. This is the strongest option for this particular identifier.
Tracking permission prompts. On iPhone, apps must ask before tracking you across other companies’ apps and websites. You can say “Ask App Not to Track”, and there is a setting to stop apps from even asking. When you decline, the app is not given the usable identifier.
Where to find the settings
Menu names change between versions and manufacturers, so use your settings search box as a shortcut. Searching for “ads”, “advertising” or “tracking” typically gets you there.
- On iPhone: look in Privacy and Security for a Tracking section. There is also a place to review which apps have asked for tracking permission, and a separate control for personalized ads from Apple’s own services.
- On Android: look under Privacy, or Settings and then Google, then Ads. You will usually find an option to delete the advertising ID and another for ad personalization. Some phone makers add their own ad settings too.
If your phone’s menus look different from these descriptions, search for the words above rather than assuming the feature is missing.
A reasonable approach
- Decide what you want. If you do not mind ads that are relevant, you might do nothing. If you would rather not be profiled, switch off personalization and delete or restrict the identifier.
- Decline tracking prompts by default. You can always allow one later if a feature truly needs it. Most apps work without it.
- Reset now and then. If you leave personalization on, an occasional reset limits how long one profile follows you.
- Review app permissions at the same time. Location and contacts data often matter more for ad profiling than the identifier does. Our broader discussion of app permissions explains how to review them.
- Remember accounts. If you sign in with the same email everywhere, a company that sees that email can often link activity regardless of the advertising ID.
Free apps and ads
Many free apps use advertising to pay for themselves, and the identifier is part of how that system works. If you rely on a favorite free app, consider that turning off personalization may leave you with more generic ads but not fewer of them. If ads or data practices bother you, a paid version or a different app is sometimes available. That tradeoff is explored further in the article on free app data.
Settings, platform rules and legal requirements change over time, so check the current options on your own phone. The principle stays the same: the advertising ID is a label you are allowed to manage, and a few minutes in settings gives you more control over it.