Cross-device tracking explained: what is it and how it works

People today constantly switch between devices, making it challenging for businesses to track user behavior accurately across different platforms. So, how do you keep up? Cross-device tracking is the answer. This post will explain how it works and share best practices to help you track users smoothly and keep your data reliable.

Сross-device tracking monitors user behavior across multiple devices like smartphones, tablets, and desktops. It works like this: it connects user data from different devices with the help of other identifiers. Such identifiers include unique device IDs, cookies, login information, etc.

Let’s imagine a situation where multi-device tracking takes place. Users see a product they like on an ad banner when running errands. They google the product on their mobile device. Later that day, a user sits at his laptop, studies the previously discovered product, and makes a purchase. 

Cross-device tracking methods can help a business link those actions together, not perceiving this one user as two separate individuals. This way, a business gets a complete vision of the user journey and uses it to polish its marketing and sales strategies. GA4's new measurement model allows for tracking web and app data simultaneously through data streams, giving a comprehensive view of a user's journey across different devices.

Cross-device tracking empowers marketers. This method gives them more profound insights into user behavior, allowing them to create better-targeted ad campaigns. It also enables advanced personalization and precise campaign measurement, giving marketers control and confidence in their strategies.

Cross-device tracking allows businesses to show users the most relevant ads regardless of their current device. This customer-centric approach ensures that companies can deliver consistent multi-device experiences across different platforms, prioritizing users' needs and preferences and leading to better commercial results.

Cross-device data tracking became a hot topic when mobile and smartphone technology advanced significantly. According to research by the Pew Research Center, an average U.S. household with internet access had 17 connected devices in 2023. So, it's not surprising that anyone uses multiple devices during the day, such as mobile phones, tablets, laptops, and desktops. As shown in the example below, there are clear tendencies about what tasks users find are better to complete on the "big internet or the small internet" and how different generations approach it.

One thing is sure—most people on the internet are actively using more than one device at the same time or throughout their day, so cross-device tracking and cross-device targeting are ways in which a business can better tailor its offerings to these clients.

It all boils down to this: consumers increasingly shift to multi-device usage. Brands that adopt multi-device tracking demonstrate their adaptability to changing consumer behavior. This enhances customer experience and improves ad targeting, reassuring businesses about the effectiveness of cross-device tracking.

Cross-device tracking has some substantial benefits. The following infographics show the major ones.

Let’s look at each of the advantages of multi-device tracking.

1. Improved user experience (UX) across multiple devices. When you get a comprehensive view of user experience across different platforms, you can customize your brand message for every platform to ensure it reaches your target audience most effectively. Moreover, cross-device analytics is vital for spotting places where users' interactions with your brand are ineffective. Based on this data, you can decide how to improve them for better results. Or, you could shift your priority to more impactful platforms.

2. Personalization and multi-device targeting. Cross-device targeting allows advertisers to better target users based on their behavior on different devices. A consistent message from a business on other devices is more likely to result in a conversion. For example, when a user looks up a product on their mobile phone and later researches it and makes a purchase on his desktop, cross-device conversion tracking ensures that the marketing efforts of the same user are recognized on two different devices.

3. Cross-device attribution and analytics for better ROI are other benefits of cross-device tracking. It allows businesses to improve marketing campaigns' return on investment (ROI). Cross-device attribution will enable marketers to accurately credit each interaction on each device and channel that influenced the conversion. It improves ROI by providing accurate insights into how each touchpoint contributes to conversions. This approach helps businesses spend their ad budget more wisely by targeting the devices and channels that lead to the most sales while improving reports and making finding and keeping valuable customers more straightforward.

4. Help businesses polish their multi-platform ad campaigns. By understanding how customers interact with their brand on each platform, advertisers can deliver more relevant ads based on the user's behavior and preferences, ensuring a consistent experience across devices. This boosts engagement and helps more people take action because the ads reach them on a suitable device at the right time. Cross-device targeting also makes ad campaigns more unified and effective, reaching a larger audience and getting better results.

Sounds good, right? Now, let's explore how this magic of staying in touch with users, no matter what their device, actually works. 

There are different approaches to cross-device analytics, each with pros and cons. One method uses exact data, like login details, to accurately follow the same user on other devices. Another look at patterns, like the type of device or how someone uses it, to make guesses about whether it's the same person, etc. Both methods are useful, but the choice depends on how accurate the tracking needs to be and what information is available.

Deterministic tracking uses unique identifiers like user logins to link devices. It evolved as an alternative to cookie-based tracking when websites started inviting visitors to create accounts for their websites or apps. This way, each of the user's devices can be linked to the same user. 

For example, when you sign into Netflix on your TV and later use the Netflix app on your phone, deterministic cross-device tracking knows it's the same person or user. This happens because both devices use the same login information, making it easy to track you as one person across different devices.

Deterministic tracking is helpful and very accurate, but it has some limitations. It only works for people who have already signed up or logged in, and it can only track new visitors with an account or a unique ID.

Probabilistic tracking guesses if the same person uses different devices by looking at patterns. It doesn't use exact data like a login but instead looks at the type of device, location, or browsing habits. These clues make an educated guess whether it's the same user across devices. This method isn't as exact as deterministic tracking, but it helps track users who haven't logged in or created an account.

Probabilistic tracking analyzes anonymous data points that don't directly identify a person but can suggest that different devices belong to the same user. These data points include:

1. 1.
   Device type (such as phone, tablet, or computer)
2. 2.
   Browser type and version
3. 3.
   Operating system (like iOS or Android)
4. 4.
   IP address
5. 5.
   Location data (city or region)
6. 6.
   Time of activity (when the device is used)
7. 7.
   Browsing behavior (such as visited websites or actions taken)

By combining these data points, probabilistic tracking makes a good guess about whether the same user is active on different devices.

A user journey is never linear, so they can go through different touchpoints and devices before making a purchase, and cookies alone are not enough to track the whole user journey. When it comes to cookies alone, there isn't anything they can do for cross-device attribution alone. They store user data within one device on a browser, so they can't be transferred across devices. 

GA4 has four identity spaces for tracking users: 

• User-ID (tracks signed-in users across devices)
• Device ID (tracks users on one device)
• Google Signals (enables user of User-ID for cross-device measurement in conjunction with logged-in Google accounts)
• Modeling (predicts behavior when cookies are blocked). 

While Reporting Identity options include:

• Blended (uses User-ID, Device-ID, then Modeling)
• Observed (uses only User-ID and Device-ID)
• Device-based (only uses Device-ID)

This means that your only direct lever on cross-device tracking is providing a User ID (and enabling Google Signals), so the deterministic approach is described above. Cross-device tracking based on User ID is among the most effective identification method. However, it requires a custom implementation. It is available only for websites and apps where users fill in their data. Behavioral modeling revolves around compensating unconsented data, and there are no clear indications that the machine learning involved has anything to do with cross-device. 

Tracking often fails when user identifiers are missing across sessions or devices. Even if a user is partially identified (e.g., email collected on one visit, but missing on another), systems may not be able to stitch events together.

To solve this problem, Stape has developed the Enricher power-up. It stores selected user data from incoming requests and reuses it to enrich future events when information is missing.

Enricher builds a user data layer using cookies and/or Stape Store (data storage solution developed by Stape). When a user returns and triggers a new event without identifiers (such as email, phone number, or name), the power-up looks for any available identifiers:

1. 1.
   email
2. 2.
   _sbp (Stape's app cookie)
3. 3.
   FPID
4. 4.
   _ga (GA4 client ID)
5. 5.
   _dcid (Stape Data Client ID)
6. 6.
   X-Stape-User-Id

If there're such identifiers, the power-up automatically supplements the request using previously collected data. It means a user can be recognized even if they switch devices or return later without logging in, as long as some identifier was captured earlier.

For more details on power-up, as well as the configuration guide, follow the documentation on Enricher.

Several platforms provide the identifiers and infrastructure needed for cross-device tracking, each suited to different use cases:

The right platform depends on whether a business needs deterministic accuracy (requiring logins), probabilistic reach (covering anonymous users), or a combination handled through server-side infrastructure.

Сross-device tracking helps businesses stay connected with users as they move between devices, allowing for a more complete understanding of their behavior. By leveraging a mix of tracking methods, companies can deliver relevant content, improve targeting, and refine their marketing strategies.