The folks over at makeuseof have a great article on how to install and configure Nagios on your Raspberry Pi. If you’re not familiar with Nagios, there’s a brief tutorial on what some of the basic settings are.
“Whether you want to keep an eye on devices on your home network or wish to monitor the performance of your website, the open source Nagios monitoring tool should be your first port of call. Although you’ll need a Linux box, the Nagios software is quick to install and straightforward to configure.”
This is a powerful tool and it’s an ideal application for the Raspberry Pi.