Because the tool checks page content it can even detect when the server is OK, but a site or page is unavailable.

There is no limit to the number of sites that can be monitored, including secure sites, and the checking frequency can be anywhere between once a minute and once a day. When a site goes down the system tray icon will change to an animated alarm and optionally you are displayed a warning message.

When a site becomes available again you can view a log to determine how long the site has been down.