Sun Microsystems FIRE V40Z - Manual (Page 179)

Appendix G Sensor Commands 157
Note – There are some sensors whose value does not change, some that are there to
provide information in the event of a problem, and others to facilitate the proper
operation of the software.
Many of these sensors do not have a related component (parent) associated with
them. For example, the die-temperature sensor for a CPU has the CPU as its parent
component, and a fan speed sensor has the fan as its parent component; the
product-id sensor, however, only reports a static value and has no parent
relationship.
This relationship establishes the component(s) which is affected by changes in the
value of the sensor. You cannot modify the thresholds for sensors without a parent
relationship since an event will never occur for these threshold crossings.