Today Amazon released another big enhancement for EC2 users, CloudWatch alarms can now be used to detect idle/unused or even underutilized instances and shut them down. Users have the option of first sending an email, shutting down the instance and/or even terminating the instance after a predefined period of time.
What does this mean? It means we can stop wasting money on instances that have been forgotten for a couple weeks, it’s also a great tool to use for keeping developer instances in check, the early email warnings provide an opportunity to prevent accidental terminations without taxing managers to monitor usage daily.
http://docs.amazonwebservices.com/AmazonCloudWatch/latest/DeveloperGuide/UsingAlarmActions.html