X-Pack has sophisticated alerting capabilities that can alert you in multiple possible ways when certain conditions are met. It gives tremendous flexibility in terms of when, how, and who to alert. 

You may be interested in detecting security breaches, such as when someone has five login failures within an hour from different locations or finding out when your product is trending on social media. You can use the full power of Elasticsearch queries to check when complex conditions are met.

Alerting provides a wide variety of options in terms of how alerts are sent. It can send alerts via email, Slack, Hipchat, and PagerDuty.