|Data.com Duplicate Management available in: Professional, Enterprise, Performance, Unlimited, and Developer Editions|
Duplicate rules tell Salesforce what action to take when users attempt to create records that may duplicate existing Salesforce records. For example, the duplicate rule could block users from saving the possible duplicate record or allow them to save it anyway.
By default, duplicate rules run when users save records. You can change this behavior for Salesforce1 so that duplicate rules run as users complete fields on the record instead. This reduces data entry time, which is always desirable on a mobile device. In the full Salesforce site, from Setup, click . In the Duplicate Rule Settings section, select Run duplicate rules when users complete fields.
For more information about duplicate rules, including how to set them up, see the Duplicate Management entry in the Sales Cloud section of these release notes.