You check out a pair of shoes online once. Then, for the next few days, those same shoes seem to follow you everywhere. You see them on a news website, inside an app, or even while watching videos.
It can feel like your phone is listening to you. But in most cases, the explanation is less mysterious — and arguably more annoying. Advertisers use tracking technologies to remember that you showed interest in something and then use that information to decide which ads to show you later.
The practice is commonly called retargeting or remarketing.
The short answer
Retargeting is a form of online advertising that targets people who have previously interacted with a business. You might have visited a website, looked at a product, searched for something, or added an item to your shopping cart.
The website or advertising platform can then use information about that interaction to place you into an advertising audience.
That is why the shoes you looked at yesterday can suddenly appear on completely unrelated websites.
But there is an important distinction: seeing an ad for something you discussed does not automatically mean your phone was listening to you.
Step 1: A website records what you looked at
When you visit an online store, the website can use technologies such as cookies, pixels, local storage, or other tracking mechanisms to remember your visit.
A tracking pixel is a tiny piece of code or a request to an outside server that can tell a website or advertising service that a particular page was viewed.
For example, you visit a page selling red running shoes. The website may record that you viewed the product.
A cookie can then store an identifier in your browser that helps the website recognize the browser when you return.
Think of it less like a note saying “this person is John” and more like a temporary label saying:
“This browser showed interest in running shoes.”
Modern tracking is often more complicated than simply placing a cookie. Depending on the service, information can also be associated with an account, advertising ID, first-party data, or activity recorded on the company’s own servers.
Step 2: The information can be used for advertising
Now suppose you leave the shopping site without buying anything.
Later, you visit another website that displays advertising. If the advertiser or advertising platform has a way to recognize that your browser or account belongs to an audience interested in those shoes, it can potentially serve you an advertisement for them.
This is why a shoe advertisement can appear while you’re reading a news story that has absolutely nothing to do with shoes.
The news website doesn’t necessarily know that you were shopping for shoes. The advertising system may simply have determined that your browser or account belongs to a particular advertising audience.
Step 3: An ad auction can happen in milliseconds
Modern online advertising can work incredibly quickly.
When you open a page containing an advertising slot, information about the available ad placement can be sent to an advertising marketplace. Eligible advertisers may compete to display an ad based on factors such as the audience, page, campaign settings and expected value.
The process can happen in milliseconds.
By the time the webpage finishes loading, the winning advertisement may already be displayed.
So when you see those shoes appear on another website, there may have been an entire automated advertising process behind that single impression.
What are first-party and third-party cookies?
This is where things get a little more complicated.
A first-party cookie is generally created by the website you are visiting. It can be used for things such as keeping you logged in, remembering your shopping cart, saving preferences, or measuring activity on that site.
A third-party cookie is associated with a different domain or service from the website you are currently visiting. Historically, third-party cookies became an important technology for tracking users across different websites and building advertising profiles.
But third-party cookies are no longer as powerful as they once were.
Safari and Firefox have long restricted third-party tracking, and other browsers have introduced additional privacy protections. Google also changed course on Chrome’s third-party-cookie plans. Rather than completely removing third-party cookies from Chrome as originally planned, Google announced in 2024 that it would pursue a user-choice approach instead.
That doesn’t mean tracking has disappeared. It means advertisers have increasingly had to rely on other methods.
Ads can follow you without third-party cookies
Even when third-party cookies are blocked, companies can still use other technologies and data sources for advertising.
Logged-in accounts: If you are signed into a shopping website, social network, or other service, the company can associate activity with your account. This doesn’t require a third-party cookie to remember everything.
First-party data: A retailer can use information collected directly from its own customers, subject to applicable privacy rules and user choices. For example, a store may know that a customer previously viewed or purchased a particular category of products.
Email-based audience matching: Advertising platforms can allow businesses to use customer information, such as email addresses, to create or match advertising audiences. The process generally uses hashing and matching mechanisms rather than simply exposing customer email addresses to advertisers.
Server-side tracking: Some companies send measurement or conversion information directly from their own servers to advertising or analytics platforms. Because this happens between servers, it is different from traditional browser-based tracking and may not be stopped simply by blocking a browser cookie.
Browser and device signals: Websites can also receive information about the browser, device, operating system and other technical characteristics. Some techniques attempt to combine these signals to recognize or distinguish users, although modern browsers are increasingly designed to limit invasive fingerprinting.
So why does it feel like your phone is listening?
This is one of the creepiest parts of online advertising.
You mention a product to someone, and a few hours later you see an advertisement for it. It is natural to assume your phone must have heard the conversation.
But there are many less dramatic explanations.
You may have searched for the product earlier and forgotten about it. You may have clicked a related link, watched a video about it, or visited a website selling it.
Someone else in your household may have searched for the same thing. Your activity across different services may also have created an advertising profile that predicts your interests.
And sometimes, it really is coincidence.
There are thousands of advertisements you see every week that have nothing to do with your conversations. The strange matches simply stand out because they feel unusually personal.
That doesn’t mean online tracking isn’t real. It absolutely is. But an unexpected advertisement by itself isn’t proof that your microphone was secretly used to target you.
Can websites see everything you do?
No.
A website generally cannot simply see your entire browsing history because you visited it once. Websites are separated from one another by browser security rules, and access to information is limited.
However, companies can collect significant amounts of information through their own websites, apps, advertising systems, analytics tools and partnerships.
The amount of information available depends on the service, what you do while logged in, which tracking technologies are allowed, your browser settings, your device settings and the permissions you have granted.
This is why privacy settings matter.
How can you reduce targeted advertising?
You don’t have to completely disappear from the internet to reduce tracking.
Start by enabling your browser’s built-in tracking protection. Browsers such as Firefox, Safari and Brave offer stronger privacy protections than a default browsing setup in many situations.
You can also periodically clear cookies and site data, although this can log you out of websites and won’t stop every form of tracking.
When websites ask for permission to use non-essential cookies, review the options instead of automatically accepting everything.
Check the advertising and privacy settings on major accounts you use, including Google, Meta and Apple, and disable personalized advertising where appropriate.
On your phone, review app permissions and advertising-related settings. Location access is particularly important because location information can reveal a great deal about your behavior.
Private or incognito browsing can reduce some local browser storage, but it does not make you anonymous. Your internet provider, employer, websites, logged-in services and other parties may still be able to observe certain activity.
Finally, remember that staying logged into multiple services makes it easier for those individual companies to connect activity with your account.
Can you completely stop retargeting?
Not completely.
You can significantly reduce tracking, but there is no single switch that makes you invisible to every advertising system on the internet.
Blocking third-party cookies helps. Privacy-focused browsers and extensions can help further. Limiting account-based tracking and unnecessary permissions can also reduce the amount of information companies can use.
At the same time, advertising technology continues to evolve. As browsers restrict older tracking methods, advertisers increasingly rely on first-party data, account-based systems, server-side measurement and other privacy-preserving or alternative techniques.
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That’s why the disappearance of third-party cookies doesn’t mean targeted advertising will disappear.
The bottom line
When a pair of shoes you looked at yesterday suddenly appears in an advertisement today, it usually isn’t magic — and it doesn’t necessarily mean your phone was listening to you.
It is more likely that an advertising system received a signal that you were interested in those shoes and used that information to place you into an advertising audience.
Cookies were once a major part of this process, but modern advertising is much broader than cookies alone.
The good news is that you have some control. Browser privacy settings, cookie choices, account controls, app permissions and careful decisions about what you share can all reduce how much information is available for personalized advertising.
The internet may not forget everything you look at, but you can make it remember considerably less.
How Does a Website Know You Looked at Something Yesterday and Show You Ads for It?
