Zabbix

As much as I love Nagios and its core design, I think there's a better way to put monitoring in place.

Meet Zabbix. It will monitor a lot of aspects of your device or virtual machine out of the box as soon as you've installed its agent or just set-up the correct snmp settings.

Zabbix comes natively with HA features, it uses proxy servers to overcome the geographic hurdles and more. You can have multiple users with different roles and accesses and even set-up a guest account to follow the state of things you monitor.

I have used Zabbix to monitor desktops, servers, IoT, embedded machines and more. You can have the Zabbix server connect to your devices or establish a "call home" feature as needed. You can make the communication between the server and the host secure by using encryption methods.

If your current monitoring solution is becomming out of breath and struggles to meet your demands, just switch to Zabbix.