Automate security monitoring by setting up in-app and email alerts for conditions of your choosing. Indicate what changes you want to be alerted of, how you want to be alerted, and who receives the alert.
Where: Security Center is available in Enterprise, Performance, Unlimited, and Developer editions as an add-on subscription.
Who: This change is available to customers who purchase Security Center and Event Monitoring add-on subscriptions.
How: From the Security Center app in your parent tenant, click the Alert Settings tab. Click New Alert, and follow the instructions to define your alert details like triggers and thresholds. For example, receive an alert if the number of users with the Modify All Data permission in any tenant reaches more than five.
Create Alerts for Changes to Your Security Configuration (salesforce.com)