Website hosting companies always promise 99.99% uptime. The truth is that few companies ever reach that. No one likes to see their website go offline. If any of your websites go down, it is important that you know about it as soon as possible so that downtime can be kept to a minimum.
An effective way to do that is to use a website uptime monitoring service. These services will alert you as soon as your website goes offline. They can do this via email, text message (SMS) or even a telephone call.
This page lists good website uptime monitoring services that are available to you.