An advertising identifier (AdID) is a resettable, device-level ID that lets advertisers recognise a device across apps without using a permanent identifier such as a hardware serial number. On Android it is the Google Advertising ID (AAID); on Apple devices the equivalent is the Identifier for Advertisers (IDFA). The umbrella term for both is mobile advertising ID (MAID).
What it is used for
Advertising identifiers underpin three common jobs: building audience segments, capping how often someone sees an ad, and attributing an outcome back to the campaign that caused it. Because the same ID appears across apps on a device, activity can be joined together without needing a name, email address or phone number.
Why it is resettable
The defining property of an AdID is that the user controls it. It can be reset at any time, which breaks the link to previous activity, and it can be switched off entirely. On iOS, Apple’s App Tracking Transparency framework means the IDFA is only available after the user explicitly opts in, which sharply reduced its availability from 2021 onwards.
Is an advertising ID personal data?
Under the GDPR, an advertising identifier is generally treated as personal data, because it singles out a device and can be combined with other information to identify a person. It therefore requires a lawful basis for processing, which in practice usually means consent.
Related: read how Tamoco sources consented location data.
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