The sensitivity option allows you to control how many monitoring "nodes" need to report the same failure condition before it is counted as an outage.
You have a website running with Acme ISP, and a an uptime test configured with a sensitivity of two.
A monitoring node based in Azure EU (Ireland) identifies that your website is inaccessible, but another located in our data centre in the Berkshire area indicates that it is available. No alert would be triggered.
If the sensitivity was set to one, you would have received an alert and it would have been logged as an outage.
At present we are conducting all monitoring tests from three locations: Azure, Amazon Web Services and our own co-located data centre in Berkshire. As such, we recommend a setting of two or LESS for the sensitivity.
Higher numbers for sensitivity will reduce false alarms, but may mean you miss events that would impact a sub-set of your potential visitors.
Please note, if you are hosting on Azure or AWS, you do NOT want to set a sensitivity level of three as this will NEVER generate any alerts.