For years, cookies were the glaring blind spot in mobile advertising. The slivers of code that track user data across the web don't work well on phones. Other tracing solutions are piecemeal. So advertisers have sprayed device screens with banner ads and prayed for sales.

But major tech companies are looking to completely bypass the cookie, aiming to track consumers on their phone and every other device they use.

Last year, when Facebook bought ad server Atlas Solutions, from Microsoft, it wasn't forthcoming about its plans. Now, it's preparing to pitch the tool as a "cross-platform solution" that will eventually make the cookie obsolete, according to Graham Mudd, Facebook's director of advertising measurement.

"Our big mistake on desktop was using metrics and attribution that only worked on desktop," Mr. Mudd said. "That limited dollars flowing to digital in a very meaningful way."

Other tech giants are shedding the desktop tracker, in favor of enclosing users in their universes. Microsoft and Apple recently introduced traceable unique identifiers for their smartphones and tablets.

Google said in March that its email mobile app is now automatically integrated with its other applications on the rival iPhone (as well as on the Android platform). On April 2, Google bowed Universal Analytics -- a version of its campaign-tracking tool for multiple devices with a single-user ID.

With large logged-in audiences, these tech players have an inherent advantage when it comes to tracking users across devices.

Google Analytics is the sharpest tool for tracking ad campaigns but "it just showed us a partial aspect of the story," said Feras Alhlou, president of digital analytics firm E-Nor, which was among the Google partners offered an early peek at the new product.

In a campaign with digital-recorder company TiVo, E-Nor measured a leap of 40% in views and mobile-app sessions, as the audience bounced between screens. InfoTrust, another ad manager using the product in beta, lauded the ability to eye the same customer on desktop and mobile for the first time.

"If I can shift the approach from visits to visitor," Mr. Alhlou said, "we get a lot more visibility."

Mr. Mudd calls this a "census-level" measurement. When it launched its ad service, Facebook implanted its own software-development kit tracing smartphone behavior. In the past year, it has signed deals with three data brokers, Acxiom, Datalogix and Epsilon. Geo-location abilities, Mr. Mudd said, are coming soon.
With its cross-screen ambitions, Facebook is aiming to move to the head of the industry; Nielsen plans to integrate mobile metrics with TV brand equity later this year.

Sean O'Neal, president of Adaptly, a mobile-ad platform that works with Facebook, said the social network has an edge in the cross-screen race. At home, he uses Google's web browser; at work, another; and with his iPhone, a third. But on each device he's signed into his social-media account.

"The universal ID today in the world is your Facebook log-in," he said. "This industry-wide challenge of mobile tracking has sort of quietly been solved, without a lot of fanfare."