With AWS Budgets Alerts you can now automatically monitor Reserved Instance coverage

You can use AWS Budgets to monitor how much of Amazon ElasticCache, Amazon RDS, Amazon Redshift and Amazon EC2 usage is covered by reservations and you can also receive alerts when the coverage falls below the threshold is defined. Reserved Instance coverage records the number of running instances is covered by Reserved Instance and it can be measured daily, monthly, quarterly or yearly. You can configure up to five notifications per budget. Each notification can be sent to 10 email subscribers and it can be broadcasted to an Amazon Simple notification service topic of your choice.