How to set up GA4 Cross-Device Tracking in 2025

Want to understand how users interact with your brand across devices? Google Analytics 4 (GA4) offers tools to track user activity on phones, desktops, and tablets, giving you a complete view of customer behavior.

Here’s what GA4 cross-device tracking does and why it matters:

• Tracks users across devices using User-ID, Device ID, and Google Signals.
• Improves marketing accuracy by connecting fragmented user journeys.
• Helps businesses allocate budgets wisely by identifying key touchpoints.
• Simplifies analysis with reports like Cross-Device Overview and User Explorer.

Setting it up involves enabling User-ID, configuring data streams, and choosing a reporting identity (Blended, Observed, or Device-based). Follow privacy laws like GDPR by securing user consent and managing data retention carefully.

Core Features of GA4 for Cross-Device Tracking

GA4 offers a set of core features that make tracking user activity across multiple devices more seamless, providing a solid framework for analysing user behavior and improving attribution accuracy. These features are key to understanding how users interact with your business across various touchpoints.

Identity Spaces in GA4

To link user activity across devices, GA4 uses four distinct identity spaces:

• User-ID: This is the most precise method for tracking users across devices. When a user logs in to your website or app, GA4 can connect their actions regardless of the device they’re using. This is particularly useful for platforms like e-commerce sites with customer accounts, membership programs, or any service where users frequently sign in.
• Device ID: This tracks activity by identifying individual devices rather than users. While it provides insights into device-specific behaviors, the accuracy can drop when multiple users share a single device.
• Google Signals: Previously, this feature enhanced cross-device tracking by using aggregated data from users who opted into personalised ads. However, it’s no longer part of GA4 Reporting Identity since February 12, 2024.
• Modeling: When data from User-ID or Device ID is unavailable, GA4 uses machine learning to infer user behavior.

These identity spaces form the backbone of GA4’s cross-device tracking capabilities, allowing businesses to connect fragmented user interactions into a cohesive story.

Reporting Identity Options

GA4 leverages these identity spaces to offer three distinct reporting identity methods, each designed to aggregate user data differently. The choice of method affects how user metrics are calculated and presented in your reports.

• Blended: This option uses all available identity spaces in a specific order, prioritising User-ID first, followed by Device ID, and finally relying on Modeling to fill gaps. It provides the most complete view of user behavior, making it ideal for businesses that want a holistic understanding of the customer journey, even when direct identification is limited.
• Observed: This method uses only directly observable data, following the same User-ID to Device ID hierarchy but excluding Modeling. It’s a great choice for businesses that prefer to base decisions solely on verified user interactions.
• Device-based: This approach relies exclusively on Device ID, ignoring other identity spaces. While it simplifies data collection, it’s less effective for tracking cross-device journeys. It’s best suited for businesses with single-device interactions or those prioritising privacy.

For businesses with user login systems, Blended or Observed reporting identities are recommended, as both prioritise User-ID for better accuracy. On the other hand, businesses without user authentication might find Device-based or Blended options more practical.

One of GA4’s strengths is its flexibility – you can switch between these reporting identity options anytime. Changes apply retroactively and take effect immediately, allowing you to experiment with different perspectives on your data.

How to Set Up Cross-Device Tracking in GA4

To effectively track user behavior across multiple devices using GA4, you’ll need to configure three essential components. These include setting up User-ID, enabling Google Signals, and configuring data streams with the appropriate reporting identity. This process requires a technical setup, adherence to privacy regulations, and a well-thought-out tracking strategy.

Setting Up User-ID for Cross-Device Tracking

The User-ID feature is a powerful way to track users across devices, but it does require users to log in to your website or app. By assigning a unique identifier to each user, you can connect their behavior across various sessions and devices.

Here’s how to set it up:

• Generate unique and non-personally identifiable IDs for each user during the login process.
• Assign these IDs consistently and send the user_id parameter with every event in your Google Tag and GA Event Settings Variable.
• Your development team will need to push these IDs to the Data Layer and create a corresponding Data Layer Variable.
• Avoid duplicates, as they can corrupt your data. Make sure the user_id is included with every event, not just login events.

Once implemented, test the User-ID setup using GTM Preview to ensure accuracy. Keep in mind that User-IDs cannot be merged across different GA4 properties. If you want to track a user’s journey across multiple sites, use the same GA4 property for all of them.

With the User-ID configured, you can move on to enabling Google Signals for enhanced insights.

Turning On Google Signals

After setting up User-ID, activate Google Signals to gather cross-device demographic data. Google Signals leverages session data from users signed into their Google accounts who have enabled Ads Personalisation. This feature enriches your reports with demographic details and cross-device behavior.

To enable Google Signals, go to the Admin section of your GA4 property. Under Data Collection and Modification, click Data Collection and toggle on Enable Google signals data collection. You can also select specific regions for data collection if needed.

Allow about 24 hours for demographics reports to start displaying data. These reports will include details such as age, gender, interests, language preferences, and more. Be aware that enabling Google Signals can lead to data thresholding in reports, depending on privacy settings. Also, the data collected is solely for Google Analytics unless you opt into additional data sharing settings.

Setting Up Data Streams and Reporting Identity

To ensure seamless cross-device tracking, you’ll need to configure data streams and set a reporting identity. This step integrates your user tracking into a unified GA4 view.

• Data Streams: Create separate data streams for web and mobile platforms. For web, set up a stream with your domain and enable enhanced measurements. For mobile apps, configure individual streams for iOS and Android, ensuring you include the correct app identifiers and tracking parameters.
• Reporting Identity: Choose between Blended and Observed reporting identities. Go to Property Settings and select Reporting Identity.
  • The Blended option uses User-ID, Google Signals, Device ID, and Modeling for the most comprehensive tracking.
  • The Observed option relies on User-ID, Google Signals, and Device ID but excludes Modeling, focusing only on directly observable data.

Once configured, allow 24 hours for data processing. After sufficient data is collected, cross-device insights will start showing in your reports. Be sure to activate consent mode to comply with privacy standards.

Analysing Cross-Device Data in GA4

After setting up cross-device tracking in GA4, it’s time to dive into the analysis phase. This is where you uncover how users interact with your brand across multiple devices. GA4 provides a range of reports and metrics that reveal user behavior, helping you refine your marketing strategy and improve the overall user experience.

Key Reports for Cross-Device Analysis

GA4 includes several reports designed to give you a detailed look at user activity across devices:

• Cross-Device Overview: Located under Reports > Life Cycle, this report offers a high-level view of user behavior. It highlights trends like which devices users prefer for browsing versus completing purchases.
• Devices Report: Found in Reports > Tech > Tech Details, this report breaks down performance by device type, operating system, and screen resolution. It’s particularly useful for comparing mobile and desktop behavior.
• User Explorer: Available in Reports > Analysis > User Explorer, this report lets you examine individual user journeys across multiple devices.
• Cross-Device User Journeys: This report maps the entire user journey, from the first interaction to conversion. It’s especially helpful for identifying whether users start on one device and finish on another.
• Device Overlap: This report shows how many users engage with your brand on more than one device.
• Cross-Device Paths: By analysing common patterns in user journeys, such as transitions between mobile and desktop, this report provides valuable insights for design and marketing decisions.

These reports serve as the foundation for understanding how users interact with your brand across devices. To dig deeper, focus on specific metrics that provide actionable insights.

Metrics to Track for Cross-Device Analysis

GA4 offers several key metrics to help evaluate performance across devices:

• Users & Sessions: In GA4, Active Users has replaced Total Users as the primary metric. On average, small and medium-sized business websites see 1.26 sessions per user.
• Engagement Rate: GA4 prioritises engagement rate over traditional bounce rate metrics. The median bounce rate in GA4 is 45.9%.
• Average Engagement Time: This metric tracks how long users actively engage with your content. As of December 2024, the benchmark for average session duration was 2 minutes and 19 seconds.
• Conversion Metrics: Keep an eye on Conversion Rate and total Conversions to measure how effectively different devices contribute to your goals.
• Multi-Device Conversion Paths: Understanding which device combinations lead to higher conversions can guide optimisation strategies.
• Average Revenue Per User (ARPU): For users engaging across devices, ARPU is an important metric. The current average ARPU for websites managed by professional marketing agencies is $2.49.

These metrics provide a clear picture of user behavior, enabling you to craft targeted strategies.

Using Insights to Take Action

Turning data into actionable steps is the ultimate goal. Start by identifying the most common device patterns in your users’ journeys. For example, if users frequently begin on mobile but complete their purchase on desktop, optimise each platform for its strengths.

• Streamline multi-device journeys by reducing friction and simplifying conversions.
• Adjust session timeout settings to ensure long conversion paths are accurately captured.
• Track micro-conversions like newsletter signups or product views to fine-tune your sales funnel.
• Learn from examples: An online retailer used GA4 to identify key engagement and conversion points, leading to a boost in sales. Similarly, a major publisher analysed cross-device paths to design a multi-channel campaign that increased both engagement and subscriptions.
• Segment your audience: Group users based on their cross-device behaviors. Single-device users might respond better to immediate offers, while multi-device users may need more nurturing with educational content.
• Monitor trends: Watch for changes in engagement rates across device combinations. A drop in engagement could signal technical issues or a need for UX improvements.

Keep in mind that 43% of shoppers research products online before making a purchase. Use this information to create a content strategy that supports users at every stage of their journey.

Best Practices for GA4 Cross-Device Tracking in 2025

Once you’ve set up and analysed your GA4 cross-device tracking, following best practices is key to keeping your data accurate and useful. These strategies help ensure that your tracking remains effective over time, giving you a clear view of how users interact across devices. To succeed, focus on compliance, data quality, and integrating the right tools.

Data Privacy and Compliance Requirements

Privacy laws like GDPR in Europe and CCPA in California have reshaped how businesses collect and use tracking data. These regulations demand transparency and user consent, which are critical for GA4 cross-device tracking.

When using Google Signals, you must secure explicit user consent before collecting data. This involves using cookie banners and consent management systems that clearly explain what data is being collected and why. Be open about cross-device tracking and give users the option to opt out.

Your privacy policy should clearly outline your tracking practices, including the use of Google Signals and how user data is connected across devices. Using well-timed consent prompts can help improve approval rates while ensuring compliance with privacy laws.

Managing Data Retention and Quality

GA4’s data retention policies are stricter than those of Universal Analytics. For instance, GA4 limits data retention to 14 months. To keep user data fresh, enable the “reset user data on new activity” feature. Google Signals data can be retained for up to 26 months, but this period adjusts based on your overall data retention settings.

To preserve data beyond GA4’s limits, regularly export your analytics to BigQuery. This allows you to maintain access to raw, unsampled data for deeper analysis.

Data quality is equally important. Use custom alerts and validation rules to catch errors early. GA4’s built-in insights feature can also identify unusual changes and notify you of anomalies. To improve accuracy, exclude internal traffic by specifying your office’s IP addresses. Additionally, use event parameters to focus on key metrics and keep your data well-organised.

Connecting GA4 with Other Tools

Integrating GA4 with other tools can provide a more detailed view of cross-device performance. For example, linking GA4 with Google Ads lets you share audiences, track conversions more precisely, and refine bidding strategies using real-time behavioral insights. This integration also supports remarketing efforts, like targeting users who browsed products on mobile but didn’t complete a purchase, using desktop-optimised ads.

Exporting GA4 data to BigQuery opens up opportunities for advanced analyses. With custom SQL queries and predictive models, you can combine analytics with other business data for deeper insights.

Connecting GA4 to Looker Studio allows you to build interactive, real-time dashboards that merge analytics with data from CRMs, eCommerce platforms, and advertising networks. These dashboards give you a unified view of how cross-device behavior impacts your marketing funnel.

Adding Search Console to your setup offers another layer of insight, showing how organic search behavior varies across devices. This can help you fine-tune your SEO strategy to address differences between mobile and desktop search patterns.

Start with one or two integrations that align with your business goals, then expand as you become more comfortable handling the additional data. These steps will strengthen your cross-device analytics and help you make better-informed decisions.

Conclusion

Cross-device tracking in GA4 isn’t just an optional feature – it’s a must-have for getting a clear picture of your customers in today’s device-hopping world. Ignoring how users interact across multiple devices means leaving crucial parts of their journey unexplored.

As we’ve discussed, using both deterministic and probabilistic tracking methods creates a more complete understanding of user behavior. The hybrid approach is the way to go: start by enabling User-ID for logged-in users to capture precise data, and then activate Google Signals to fill in the gaps. This combination gives you a well-rounded view of how customers move through their journeys.

One major advantage? Better marketing attribution. For instance, imagine a customer discovers your product on their phone during their morning commute, dives into more research on their work computer at lunch, and finally makes the purchase on their tablet later that evening. With cross-device tracking, you can follow this entire path and allocate your marketing budget to the touchpoints that matter most.

To make the most of GA4’s cross-device capabilities, focus on key configurations. Choose the right reporting identity, set data retention policies that align with your goals, and connect essential tools like Google Ads and Search Console. These integrations can supercharge the insights you gain from cross-device tracking.

Lastly, don’t overlook privacy compliance. Implement clear consent mechanisms and transparent privacy policies to ensure you’re respecting user data. While the setup may take some effort, the payoff – genuine insights into your customers’ behavior – is absolutely worth it.