Skip to Content

How Ads Follow You from Phone to Desktop to Tablet

Advertisers are increasingly using technology that targets users across multiple devices, and it’s working.

Imagine you slack off at work and read up online about the latest Gibson 1959 Les Paul electric guitar replica. On the way home, you see an ad for the same model on your phone, reminding you this is “the most desirable Les Paul ever.” Then before bed on your tablet, you see another ad with new details about the guitar.

You may think the guitar gods have singled you out—it is your destiny to own this instrument!

For advertisers, the process is divine in its own right. Over the past year, companies have substantially and successfully stepped up repeat ad targeting to the same user across home and work computers, smart phones and tablets. With little fanfare, the strategy is fast becoming the new norm.

“You really have a convergence of three or four different things that are creating a tremendous amount of change,” says Philip Smolin, senior vice president for strategy at California-based digital advertising agency Turn. “There may be one wave that is small and it doesn’t move your boat very much, but when you have three or four medium size waves that all converge at the same time, then it becomes a massive wave, and that is happening right now.”

One of these recent waves has been greater sophistication of companies engaged in “probabilistic matching,” the study of millions of Web users to determine who is likely to be the same person across devices. For example, Drawbridge, which specializes in matching users across devices, says it has linked 1.2 billion users across 3.6 billion devices—up from 1.5 billion devices just a year ago.

Another trend making all this matching possible is the continuing transformation of Internet advertising into a marketplace of instant decisions, based on what companies know about the user. Firms you have never heard of, such as Drawbridge, Crosswise, and Tapad, learn about your devices and your interests by tracking billions of ad requests a day from Internet ad exchanges selling in real time. Potential buyers see the user’s device, IP address, browser, and other details, information that allows for a sort of fingerprinting.  “We are getting very smart about associating the anonymous identifiers across the various devices,” says Kamakshi Sivaramakrishnan, founder and CEO of Drawbridge.

For example, a cell phone and tablet accessing the same IP address at home would be one clue, as would searches for the same product. You might look for “Chevy Cruze” on your phone and then search for the same thing on your laptop. The same geographic location of the searches within a short time period, combined with other information, might suggest the same user.

In the last six months or so, these companies say they have sharply increased the accuracy of probabilistic matching. A Nielsen survey of Drawbridge data released in April found 97.3 percent accuracy in linking two or more devices; an earlier Nielsen survey of Tapad found 91.2 percent accuracy.

Another wave feeding the fast growth of cross-platform advertising is the stampede onto mobile devices. Just last month Google announced that users in the United States, Japan, and eight other countries now use mobile devices for more than half of their searches. U.S. mobile traffic soared 63 percent in 2014 alone, according to a report from Cisco.

Many consumers search on mobile devices but buy on larger-screen computers, giving advertisers ever more incentive to track across multiple screens. Ad agencies are also breaking down traditional walls between video, mobile, and display teams to forge a more integrated approach.

For example, Turn recently worked with an auto insurer’s campaign that started with a video ad on one platform and then moved to display ads on other devices. The results of such efforts are promising. Drawbridge says it ran a cross-platform campaign for women’s sandals in the middle of winter for a major fashion retailer and achieved three times greater response than traditional Internet advertising.

People who prefer not to be tracked can take some countermeasures, especially against what is called deterministic tracking. Signing into Google or Facebook as well as websites and apps using those logins confirms which devices you own.  So you can log off Facebook, Google, and other accounts, use different e-mail addresses to confuse marketers and use masking software such as Blur. “But the probabilistic stuff is really hard to stop because it is like all the detritus of one’s daily activities,” says Andrew Sudbury, chief technology officer and cofounder of privacy company Abine, which makes Blur.

People can opt out of Internet tracking through an industry program called AdChoices, but few know about it or bother.

Advertisers stress they match potential buyers across platforms without gathering individual names. “People freak out over retargeting. People think someone is watching them. No one is watching anyone. The machine has a number,” says Roland Cozzolino, chief technology officer at MediaMath, a digital advertising company that last year bought Tactads, a cross-device targeting agency. “I don’t know who you are, I don’t know any personal information about you. I just know that these devices are controlled by the same user.”

Companies that go too far risk the wrath of customers. Verizon generated headlines such as “Verizon’s super-cookies are a super privacy violation” earlier this year when the public learned that the carrier plants unique identifying codes dubbed “supercookies” on Web pages. Verizon now explains the process on its website and allows an opt-out.

Drawbridge recently started tracking smart televisions and cable boxes, but advertisers on the whole are cautiously approaching targeted TV commercials, even as many expect such ad personalization in the future. Industry officials say they want to turn up the temperature slowly on the frogs in the pot of advertising, lest they leap out and prod regulation.

Deep Dive


What’s next for AI regulation in 2024? 

The coming year is going to see the first sweeping AI laws enter into force, with global efforts to hold tech companies accountable. 

Three technology trends shaping 2024’s elections

The biggest story of this year will be elections in the US and all around the globe

Four lessons from 2023 that tell us where AI regulation is going

What we should expect in the coming 12 months in AI policy

The FTC’s unprecedented move against data brokers, explained

It could signal more aggressive action from policy makers to curb the corrosive effects that data brokers have on personal privacy.

Stay connected

Illustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at with a list of newsletters you’d like to receive.