A browser-based or mobile-app-based identifier for a unique, pseudonymous website or mobile app user.
On a website, device ID gets its value from the client ID property of the
_ga cookie. In an iOS or Firebase app, device ID gets its value from the app-instance ID, which identifies a unique installation of the app.
Device ID is one of the available reporting identity spaces.
- Data collection (opens in the Firebase Help Center)
- Automatically generated and assigned app-instance ID
- Google tag API reference