Metrics install automatically if you have Redgate Monitor installed.
If you are using Redgate’s SQL Server monitoring tool, Redgate Monitor, you can instantly install and run this metric on your servers.
This custom metric queries the default trace to find events related to Server roles being altered
Metric definition
Name
Login added to serverrole
Description
This custom metric queries the default trace to find events related to Server roles being altered
The T-SQL query that will collect data
Instances to collect from
Select all
Databases to collect from
Master
Collection frequency
60
Use collected or calculated values
Leave the Use a calculated rate of change between collections check box unchecked
Metric collection
Enabled
Alert definition
You could add an alert once the baseline for your environment has been established.