Q:

Is it possible to have a property sensor detect another property?

Is it possible to have a property sensor detect another property?
Like this:

A:

Is it possible to have a property sensor detect another property?

(I assume you want to compare on property's value with another property's value.)
No, the property sensor evaluates a single property only. 
When you want to evaluate more properties you can use the expression controller:
property_1 < property_2

or the Python controller
import bge 

controller = bge.logic.getCurrentController()
owner = controller.owner
if owner["property_1"] < owner["property_2"]:
    for actuator in controller.actuators:
        controller.activate(actuator)
else:
    for actuator in controller.actuators:
        controller.deactivate(actuator)

I hope this helps

