# Introduction

Of course, [more advanced work can be done](https://pandorafms.com/manual/!development/en/documentation/04_using/01_alerts) such as alerts on events, correlation, etc. The first alert to do is to send an email when one of the machines that are already being monitored (with the **Host alive** module) goes offline.

Pandora FMS alerts are composed by three elements:

- **Command.**
- **Action.**
- **Template.**

In this specific case we are going to use a predefined command (sending emails), we are going to modify an action that already exists (`Mail to XXX`) and we are going to use a template that also exists, the Critical condition template, that will execute the alert when the module in question appears in critical condition.

See also: "[Pandora FMS alert system (video)](https://www.youtube.com/watch?v=0_vlsrxb5Os)".