Duplicate rule scope: conditions, compared objects, and record-level security
Key Takeaway
Three settings control a duplicate rule's scope: conditions (when it runs), the matching rules' objects (which records it compares against), and record-level security (whether it respects the user's sharing access).
A duplicate rule tells Salesforce what to do when a user creates or edits a record that looks like a duplicate: alert the user, block the save, or report it. You build each rule on one object, but its scope settings can widen it. The rule can find duplicates on other objects, and it can compare against records the user doesn't have access to.
What a duplicate rule is made of
You build a duplicate rule on one object. In Setup, click "New Rule" and pick the object the rule applies to.
The rule uses matching rules to decide which records count as duplicates. Its actions decide what happens next. By default, the rule alerts users when they start to create a duplicate, and it reports on duplicates created when users create or edit records.
You can activate a duplicate rule only when all of its associated matching rules are active.