Once you add your website for monitoring, the website moniter servers send out HTTP/ HTTPs requests to your website at regular intervals of time to check if your website is accessible. 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.
The monitoring intervals range from 5 to 60 minutes or above.
You can also subscribe for weekly/daily availability reports through email. These reports includes details such as uptime/downtime charts as well the total downtime details. From the 'Reports' tab, you can view your web page availability history reports. These reports give you a very good indication of your website's performance over a specified time period.