GA4 measurement IDs (G-XXXXXXXX), what GA4 tracks, and how the audit detects it — directly installed or via tag manager.
Google Analytics 4 is Google's current web analytics platform: it measures page views, sessions, events, and conversions, and feeds Google's advertising products. It replaced Universal Analytics (which stopped processing data in 2023–2024), so a site still running only UA-XXXXXX tags is running a dead analytics setup — something the audit's identifier extraction makes visible.
Each GA4 data stream has a measurement ID of the form G-XXXXXXXXXX (e.g. G-TM6HHFGY81), embedded in the gtag.js snippet or configured inside a GTM container. The audit extracts every measurement ID it finds. Multiple IDs on one page usually mean duplicate tracking — staging and production properties firing together, or two teams each installing "their" GA4.
GA4 can be installed directly (gtag.js snippet in the HTML — visible to static scans) or deployed through Google Tag Manager (configured in the container — invisible to static scans, visible in render mode). The report distinguishes these: a direct G-XXXXXXXXXX match vs. "via Google Tag Manager (client-side tag)". If you know the site runs GA4 through GTM and the static report shows only the container, that's the expected behavior, not a miss.
The audit detects that GA4 is present and which property ID it reports to. It cannot see the analytics data itself — traffic numbers, events, conversions live inside the site owner's GA4 account and are never exposed in page HTML. The beacon report is a presence-and-configuration inventory, not a traffic report.