To recognize users across different devices, what feature must you enable?
The User ID lets you associate engagement data from multiple devices and different sessions with unique IDs.
Read more here: https://support.google.com/analytics/answer/3123662
User ID lets you associate a persistent ID for a single user with that user’s engagement data from one or more sessions initiated from one or more devices.
Analytics interprets each unique user ID as a separate user, which provides a more accurate user count in your reports.
When you send Analytics an ID and related data from multiple sessions, your reports tell a more unified, holistic story about a user’s relationship with your business.
How User-ID works
User-ID enables the association of one or more sessions (and the activity within those sessions) with a unique and persistent ID that you send to Analytics.
To implement User-ID, you must be able to generate your own unique IDs, consistently assign IDs to users, and include these IDs wherever you send data to Analytics.
For example, you could send the unique IDs generated by your own authentication system to Analytics as values for User-ID. Any engagement, like link clicks and page or screen navigation, that happen while a unique ID is assigned can be sent to Analytics and connected via User-ID.
In an Analytics implementation without the User-ID feature, a unique user is counted each time your content is accessed from a different device and each time there’s a new session. For example, a search on a phone one day, purchase on a laptop three days later, and request for customer service on a tablet a month after that are counted as three unique users in a standard Analytics implementation, even if all those actions took place while a user was signed in to an account. While you can collect data about each of those interactions and devices, you can’t determine their relevance to one another. You only see independent data points.
When you implement User-ID, you can identify related actions and devices and connect these seemingly independent data points. That same search on a phone, purchase on a laptop, and re-engagement on a tablet that previously looked like three unrelated actions on unrelated devices can now be understood as one user’s interactions with your business.