Description
This alert will run against the monitored SQL Server instance and retrieve the time each session has been blocked ("Seconds Blocked" column). It will also give some details about the blocking session in the "Message" column and this can be customized with anything else from sys.dm_exec_requests DMV.
Note that DPA includes a base alert for locking, but it uses the total amount of time for all blocking that happened. This alert is different in that it uses the blocking time of each session individually.
Alert Definition
To create the alert, click on Alerts > Manage Alerts tab and create a Custom Alert of type Custom SQL Alert - Multiple Numeric Return. Configure the alert as needed and paste in the attached SQL Server query.