When you are a webmaster and you have more than 4 or 5 sites to monitor, then this become a difficult job. You don’t know when the sites are down and what is the reason? So there is a great service I found recently. With this you can monitor the Up time and hosting features for free. That is: Are My Sites Up. With a free account here you can manage five of your sites and look after their hosting status.
They will mail you every time you got a problem in your hosting and the site is down. If you open a free account then they will check your sites at least 25 times a day. You get notification through e-mail whenever your sites are down. There is also upgradeable plan avail able for this service. But I will recommend you to use their free service first.