What it is
Targeting built on identifiers associated with a phone or connected device rather than on a page’s content or a stated interest. It underpins visit-based audiences, cross-device retargeting, and household matching on connected TV.
When it works it is genuinely powerful — the same household reached on TV, phone, and desktop, counted once.
What degraded
Platform-level privacy changes reduced the availability of advertising identifiers substantially, and app-level permission prompts cut the supply further. Coverage now varies by device mix, app usage, and market density.
The practical effect: precision claims are approximate. Dense urban markets with heavy app usage behave close to the pitch; rural markets frequently do not.
What still works reliably
Household-level matching on connected TV, which uses different signals and remains solid. Retargeting from your own site, which relies on your own data rather than third-party identifiers. And matching your customer list, which is the most durable targeting you have.
Notice the pattern: the reliable methods are the ones built on data you or the publisher owns.
How to buy it
Ask what happens when the identifier is unavailable — does the impression not serve, or does it fall back to geography? Both answers are acceptable; not knowing is not.
Then verify with delivery reports rather than trusting the plan. And do not build a strategy that only works if the precision is perfect, because increasingly it is not.