This alert will return a list of objects that have recently been modified. It uses the sys.objects table and the modify_date column for detection. This table is specific to each database, so it also loops through all non-system databases to get an instance-wide perspective.
Note: this alert will simply return the objects that were modified in some way. It will not return the details of the change. Here is an alert you can use to get detailed object changes: SQL Server Detailed Object Changes
To create the alert, create a Custom SQL - Multiple Numeric Return and make is look similar to this example: