Question from Reddit user:
Is there anyway to check what users visit a site with both mobile and desktop in gA4?
Answer from Nabil:
The short answer is:
Yes, you can check what users visit a site with both mobile and desktop in GA4, but you must first ensure you have a robust cross-platform user identification method in place, typically the User-ID feature.
Once User-ID is configured, you can use the GA4 Exploration Reports to build an Audience or User Segment that filters for users who had sessions where the Device category dimension included both “mobile” and “desktop.”
The most powerful and flexible solution to visualize this cross-device behavior is to export the raw data using the Google Analytics Data API or BigQuery to create a custom, high-fidelity report in Looker Studio.
The long answer is:
The ability to track a single user across both mobile and desktop devices in GA4 relies heavily on the quality of your user identification setup, specifically the User-ID feature.
By default, GA4 uses its “blended” reporting identity, which combines the User-ID, Google signals, device ID, and modeling, but for precise reporting on a specific user group, you need to rely on the deterministic User-ID.
This requires you to assign a unique, non-personally identifiable ID to a logged-in user and send it to GA4 with every event via Google Tag Manager.
Once this is set up, you can build a User Segment within the GA4 Exploration Reports by using conditions such as: “Include users when Device category contains ‘mobile'” AND “Include users when Device category contains ‘desktop’.” This will give you a count and details of the users who meet your cross-device criteria.
However, relying solely on the GA4 interface for complex cross-device pathing analysis has limitations, especially regarding sampling and custom visualization.
An excellent solution for detailed cross-device analysis is a custom data pipeline: send your raw data from GA4 to BigQuery using the free BigQuery Export feature.
This raw, unsampled data, complete with the User-ID, allows you to use SQL queries to identify exactly which User-IDs have sessions from both mobile and desktop devices.
From BigQuery, you can then connect the data to Looker Studio via the Looker Studio API for dynamic, custom reporting and charting of the user journeys.
Further enhancing this by using Google Tag Manager and a server-side tagging solution like Stape or Google Cloud Platform allows you to enforce the consistent setting of the User-ID and other custom dimensions, ensuring that the data flowing into BigQuery is as clean and reliable as possible, leading to the most accurate cross-device reporting available outside of building your own full-stack data warehouse.
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