Site24x7 is a hosted website monitoring service that helps webmasters ensure their websites are up and running at peak performance. The Site24x7 servers send out HTTP or HTTPS requests to your website at regular intervals of time and alerts you if it is down. Site24x7 provides 10 free SMS alerts with every account. In addition, 50 free sms credits will be added to your account when you upgrade to Enterprise account. You can also get Email alerts and Rss Notifications.

A website will be reported as Unavailable if
Website is not accessible.
Response time of the website crosses 30 seconds.
HTTP Response code of the response is 4XX or 5XX.
If the username/password is invalid in the case of authenticated websites.

You will get information if there are problems, you can react quickly before your users are affected.Site24x7 is a free service but if you want to upgrade your account you have to pay very nominal charges.

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