Think that your mobile browsing habits exist in a different world than the content and ads you view on your PC? Until recently, you’d have been correct, but now advertisers are coming up with ways to identify consumers across platforms in order to provide them with ads they might actually click on.

“Every retailer is trying to figure out cross-platform activities,” Expedia’s VP of mobile and online partner marketing tells the Wall Street Journal.

In 2012, Expedia and mobile ad tech company Drawbridge launched a trial to see if they could successfully identify users across mobile and desktop platforms.

Cookies are sent to both types of devices, allowing Drawbridge to look for signifiers — like mobile and desktop devices using the same IP address to access the Internet at the same time — to determine the probability that the devices belong to the same person. If so, then the advertiser can use all the info it gleans from one device to deliver targeted ads to the other.

It’s not all that different from marketers who only need your name and ZIP code to track your purchases from store to store. Once the tracker has sufficient information to isolate your behavior, it’s just a matter of how it uses the data.

In the Expedia case, this “triangulation” system provided the travel site with info for a group of mobile users who Drawbridge believed had just visited Expedia.com on their desktop computer. Expedia then used this info to blast out travel offers to these mobile users.

“We have seen a direct positive relationship between spending on app downloads and someone consummating a transaction,” says the Expedia VP. “Technologies like Drawbridge give me a bit of a prayer but it is still early days.”

Meanwhile, companies like Facebook, where the user has to log in on each of his devices in order to use the site, allow advertisers to target users across multiple platforms.

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