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Attribution & Measurement

Device ID

Also known asDevice IdentifierMobile Device IDAdvertising ID

A unique identifier assigned to a mobile device (or its advertising profile) used to recognize the same device across apps and sessions — the backbone of deterministic mobile attribution.

Key takeaways

  1. 01A device ID lets advertisers and MMPs recognize the same device across ad click and app install — the basis of deterministic attribution.
  2. 02Key types: IDFA (iOS advertising ID), GAID/AAID (Android), IDFV (iOS vendor-scoped), plus device-bound IDs and IP as weaker signals.
  3. 03Apple ATT (2021) gated the IDFA behind opt-in, collapsing its availability to ~20-40% and pushing iOS toward SKAdNetwork + aggregated measurement.
  4. 04Android is following with Privacy Sandbox, phasing down the GAID — the whole industry is moving from device-ID matching to privacy-preserving aggregation.

A device ID is a unique string that identifies a mobile device or its advertising profile. It's what lets an ad network, MMP, or analytics SDK recognize that the device which clicked an ad is the same device that later installed and opened the app — the recognition step at the heart of deterministic [[install-attribution]].

The main device identifiers

Mobile device identifiers compared

IdentifierPlatformScopeResettable / gated
IDFAiOSCross-app advertising IDUser-resettable; ATT opt-in required since iOS 14.5
GAID / AAIDAndroidCross-app advertising IDUser-resettable; phasing down under Privacy Sandbox
IDFViOSPer-vendor (publisher) onlyNot cross-publisher; survives without ATT
IP addressBothNetwork-level, coarseProbabilistic signal only, not a stable ID

IDFA and GAID are the cross-app advertising IDs that made deterministic attribution possible. IDFV is scoped to a single publisher, so it can't track across apps you don't own.

The privacy shift is the whole story. Before 2021, the IDFA was freely available and deterministic attribution was trivial. Apple's [[att]] framework forced an opt-in prompt, and most users decline — so the IDFA is now missing for the majority of iOS traffic. Attribution moved to [[skadnetwork]] (aggregated, privacy-preserving postbacks) and probabilistic methods. Android's Privacy Sandbox is bringing the same transition to the GAID. The net direction: away from device-ID matching, toward aggregated and on-device measurement.

Quick answers

What is a device ID in mobile?

A device ID is a unique identifier for a mobile device or its advertising profile. The main advertising IDs are IDFA (iOS) and GAID/AAID (Android), which let advertisers recognize the same device across apps for attribution and targeting. iOS also exposes IDFV (scoped to a single publisher). They're the recognition layer behind deterministic attribution.

What is the difference between IDFA and IDFV?

**IDFA** (ID for Advertisers) is a cross-app advertising identifier — the same value across all apps on the device, used for attribution and targeting, now gated behind ATT opt-in. **IDFV** (ID for Vendors) is scoped to a single publisher: all apps from the same developer share it, but it can't track across other developers' apps. IDFV survives without ATT consent; IDFA mostly doesn't.

Why does device-ID attribution still work after ATT?

For the minority of users who opt in to ATT, the IDFA is still available and deterministic attribution works normally. For everyone else, attribution falls back to SKAdNetwork (Apple's aggregated framework) and probabilistic signals. So device-ID attribution didn't disappear — it shrank to the opted-in slice, with aggregated measurement covering the rest.

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