Sensor

The term sensor is used to refer to any device which is used to scan, record, or otherwise observe any aspect of an environ surrounding a starship, station, or person. This could be as simple a device as a manual camera or light sensor, or as complicated as the many devices designed to scan many aspects of the matter and energies of subspace, space, time and stellar bodies that make up all of existence.

There are many ways to mask a sensor scan, sensor screens are the most commonly used. You can also mask a sensor scan with certain materials, or radiations. But to truly hide from a sensor scan one would actually have to change it's molecular structure.