A Sensor is a block that provides readings about the surrounding world and blocks based on what kind of SensorModule Card it has received.
Once a sensor has received a Sensor Card in its GUI, the different probes can be targeted with UP/DOWN and and the readings can be observed with LEFT/RIGHT; use PAGEUP/PAGEDOWN to scroll. Sensors can be smelted into 4 iron ingots, in effect generating EMC.
Sensors that use World, Inventory, and Proximity Cards can be placed anywhere and still function. Those that use other cards must be placed directly next to the target block (they may also be indirectly connected if the Sensor and target are connected by other blocks from the same mod as the target).
Go to ccSensors for information on how to use this with other ccSensors blocks and items.