Privacy & Tech

How does cross-device tracking connect a person’s activity?

Cross-device tracking links activity across devices, such as a phone, laptop and tablet, to the same person or household. It can help a business connect an advertising interaction on one device with a later purchase on another.

Two common approaches differ in how they establish that connection:

Approach	How the connection is made	Main limitation
Deterministic matching	Uses a direct link, such as the same signed-in account on two devices.	A shared account may represent more than one person.
Probabilistic matching	Estimates connections using signals such as network information and usage patterns.	The inferred connection may be incorrect.

The FTC’s report on cross-device tracking explains these approaches and their privacy implications.

Cross-device tracking differs from cross-site tracking: one concerns movement between devices, while the other concerns activity across websites. A system may do both.

These connections often form part of identity resolution. Removing cookies from one browser does not necessarily remove account-based links or records already held elsewhere. Privacy information and user controls should clearly explain the scope of the tracking and the choices available.