Many factors contribute to a healthy sensor. Perch constantly looks at metrics around disk, CPU and memory utilization to keep your sensor ship-shape.
In addition to metrics, the application is constantly considering the state of network health and the status of required applications.
The sensor health page gives a high-level overview of the rules that the sensor is running, alert levels, as well as information into how many devices are on a network and visible to the Perch sensor.
To view sensor health, click on the name of that sensor in the sidebar.