Passive sensor

A passive sensor is a device aboard starships and space stations that is used to scan, record, or otherwise observe any aspect of a surrounding environment. It is less obtrusive than active scan, and may not be detected by the subject being sensed. At it’s simplest, passive is scanning without transmitting.

This type of sensor can only detect an object with this method when it observes objects emitting radiation, or when radiation is being reflected off an object by a source that is not doing the scan.

This is in opposite to active scan, where the sensors actually emit a source of radiation.