What are the identification techniques on mobile applications?

Our SDKs systematically base their measurements on first-party identifiers, since mobile applications cannot manage cookies.

Identification techniques are necessarily different between web and app interfaces. Web-based interfaces deposit cookies carrying unique identifiers in a visitor's browser. Apps push an identifier into the hit from the device, through a method included in the SDK.

Default identifier

By default, both the iOS and Android SDKs generate their own UUID, a random unique identifier stored on the device and sent with every event (the idclient field). This is the recommended option: it doesn't depend on advertising permissions and keeps counting visits and visitors reliably.

You can change which identifier the SDK uses through the visitor ID type setting, but the available values differ by platform.

All iOS identifiers

Set with the visitorIdType configuration (withVisitorIdType).

Value	Identifier	Description
`uuid`	UUID (default)	A unique identifier generated and stored by the SDK. Not shared with other apps.
`idfv`	IDFV (Identifier for Vendors)	An Apple identifier shared by all apps from the same vendor on a given device. Resets when the user removes all of that vendor's apps.
`idfa`	IDFA (Identifier for Advertisers)	An Apple device-level advertising identifier. It requires the user's App Tracking Transparency (ATT) authorization; without it, the value is unavailable (zeroed).
`custom`	Custom	An identifier you set yourself (`visitorId`), for example to reconcile with your own user base.

All Android identifiers

Set with the visitorIDType configuration (Configuration.VisitorIDType).

Value	Identifier	Description
`UUID`	UUID (default)	A unique identifier generated and stored by the SDK. Not shared with other apps.
`GOOGLE_ADVERTISING_ID`	GAID (Google Advertising ID)	Google's device-level advertising identifier. The user can reset it or opt out of ad personalization. Requires the `play-services-ads-identifier` library.
`HUAWEI_OPEN_ADVERTISING_ID`	OAID (Open Advertising ID)	Huawei's equivalent advertising identifier for Huawei devices. Requires the `hms-ads-identifier` library.
`ADVERTISING_ID`	Advertising ID	Uses whichever advertising ID is available on the device (Google or Huawei).
`CUSTOM`	Custom	An identifier you set yourself (`customVisitorId`), used only when `visitorIDType` is `CUSTOM`.

Good to know

Advertising identifiers (IDFA, GAID, OAID) depend on user consent and can be reset or turned off by the user, which fragments visit and visitor counts. For stable measurement, keep the default UUID.
Android ID is no longer offered as a visitor identifier since Android SDK 3.3.0, in line with Android's guidelines on user identifiers.
For the full setup, see the developer documentation on Visitor identification and the iOS and Android SDK configuration pages.

Last updated: September 23, 2026