Are My Sites Up? is a great tool that checks your website and notifies you by email or text message if your site goes down. Very simple, yet incredibly powerful.
The site has an intuitive interface. At a glance you can see if your site is up, down, or timed out the last time it was checked. If there's a problem, Are My Sites Up? will give you as much information as possible about the error code it encountered.
The free account lets you monitor up to 5 sites at a time, with alerts being sent out by email and SMS. Premium plans include more frequent checks, RSS site monitoring, secure site monitoring and Twitter integration. The most expensive plan is $95 per year and it can monitor up to 100 sites at once.
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