An ad blocker is a browser extension, browser feature or network tool that blocks ads and tracking scripts. For advertisers, it means conversions from those users often never reach the ad platform.
How does an ad blocker work?
Ad blockers rely on filter lists of known advertising and tracking domains, such as connect.facebook.net for the Meta Pixel or Google Ads domains. When a page requests a script from one of them, the request is dropped.
Common types:
- Browser extensions like uBlock Origin or Adblock Plus
- Browsers with built-in protection like Brave, or Firefox with Enhanced Tracking Protection
- Network-level blockers like Pi-hole or DNS services that stop requests before they leave the device
What do ad blockers mean for advertisers?
Every tracking pixel is client-side tracking: it runs in the browser, so it can be blocked. When a user with an ad blocker converts, the platform never sees the event. The result:
- Fewer reported conversions than actually happen
- Skewed optimisation, because the algorithm only learns from users without blockers
- A reported CPA that looks higher than reality
How much signal loss you face depends heavily on your audience. B2B and tech audiences on desktop tend to block more than mobile users.
The most effective countermeasure is server-side tracking: the event is also sent from a server to the platform's Conversions API. That server-to-server request never passes through the user's browser.
Example
A visitor running uBlock Origin fills in your contact form and has accepted marketing in the cookie banner. The Meta Pixel is still blocked. With a parallel request through the Meta Conversions API, the lead event still reaches Meta, and deduplication makes sure it is counted once if the pixel does fire.
Ad Blocker with LeadSignal
For Meta, LinkedIn and TikTok, LeadSignal sends events server-side through each platform's server API in parallel with the browser pixel, deduplicated via an event ID. That way conversions from users with ad blockers still arrive, as long as consent was given. Google Ads currently runs browser-side in LeadSignal. For the Meta setup, read our Meta Conversions API setup guide.