Sensor technologies are the topic for elements which delivers a signal. It could be a light barrier or an electrial switch. The important thing is, that they transform a physical power to show the control unit a change in the system.
an example:
explanation for the example:
Here the switch worked as a sensor. He tranforms the mechanical enegery to an electrial current flow. The diffrence between an electrical switch and a light barrier is, that a an electrical switch needs a human who do the mechanical enegery and a light barrier works autonomical because it only needs light. Both just tranform the physical enegery they get to an electrical flow.
sensor technologie