From AlertFox Website Monitoring
Response time is a top factor for most visitors in choosing a website. For many visitors, response time is even more important than price or content quality.
The HTTP Sensor does not just ping a website, but rather monitors web page uptime and performance. It loads the complete website without images and measures the load time. It reports an error if the page load time exceeds the specified timeout limits.
Our Check Host tool is based on the HTTP Sensor.
HTTP sensor-specific settings are described here. For general sensor settings, please see Sensor Settings.
A keyword check ensures that the right page is displayed, not just any page. This way, you can detect error pages or defaced pages easily and distinguish them from the correct page.
The HTTP sensor checks for the keyword on the website and in the page source, and triggers an alert if the keyword is (not) found. The keyword can be any word on the HTML page or in the page title. For example, if you test http://www.alertfox.com/, a good keyword would be "AlertFox" or "Powerful".
See also: How to monitor HTTPS websites?