Sensor modules were the primary components of scanners aboard starships, space stations, and other installations.
The location of the sensor module on the primary hull of the Enterprise-B
In 2293, the location of the sensor module on the primary hull was labeled in the USS Enterprise-B master systems display on the ship's bridge. (Star Trek Generations)
In 2370, the crew of the USS Enterprise-D installed multiphase buffers on their sensor modules, in an attempt to increase sensor efficiency while searching for the missing medical transport, the Fleming, in the Hekaras Corridor. (TNG: "Force of Nature")