Sensor

"The sensors are placed. I'm going back."

A sensor was one of a wide range of complex devices that helped gather information about a given subject. Sensors could range from simple handheld devices to more complex technology like tachyon detectors found on starships.^[2]^[3]

Sensors could operate by a variety of different methods, such as detecting electromagnetic radiation, gravitational disturbances, nuclear forces or subspace. Sensors may detect objects by motion or vibration, through changes in heat or pressure, or by sniffing out trace chemicals. Despite their advanced nature, sensors could be fooled by natural phenomenon including solar radiation, hydrogen clouds, and asteroid fields. They could also be defeated by electronic countermeasures such as sensor jammers and cloaking devices.^[2]^[4] Ships such as the VCX-100 light freighter Ghost were named for their ability to sneak past Imperial sensors.^[5]

Sensors could be divided into two categories, active or passive. Active sensors, also called search-mode sensors, detected targets by emitting controlled bursts of energy and then detecting when it reflected or "bounce" off of a target. While this allowed for detailed scanning of a target, the emitted energy would easily alert someone to its source, and their operation required relatively large amounts of power. Active sensors could be set to one of three modes:^[2]

Scan Mode: In this mode the sensor scanned the entire area around itself but could provide only basic information. Any potential hazards which were discovered triggered a warning signal to warrant a closer look.
Search Mode: When set to this mode the sensor would only look for a specific type of target as indicated by the sensor's operator. For example, ships flying in formation may set their sensors to search mode so that they only focused on specific areas. When working with a navicomputer, search mode could also help plot an emergency escape route.
Focus Mode: Used to concentrate on a specific area selected by the operator, this mode could provide much more detailed information about the scanned area compared to the other modes. However it was blind to anything outside its designated scope.

The second type were passive sensors, which did not emit energy and could only detect targets by the energy they emitted themselves. This did mean they required less power and were more difficult to detect when operated though.^[2]

Examples of sensors for personal use ranged from simple telescopes and macrobinoculars to more complex devices like electrobinoculars and radiation sensor. Droids could also possess a wide array of sensing devices. Imperial Probe droids for example could scan for objects using visual, ultraviolet and magnetic imaging devices.^[2]^[6]

Many vehicles, particularly military types, were also equipped with a wide variety of sensors. Tanks such as the AAT might possess rangefinding devices, while many walkers like the AT-AT and AT-ST possessed terrain sensors in their feet in order help with finding sure footing. Some like the HAVw A6 Juggernaut carried special headlights that scanned for targets using both visible and invisible light.^[7]

In general, starships carried sensors which could scan for objects across a wide spectrum.^[7] Examples of common sensors found on starships include electro-photo receptors, dedicated energy receptors, full-spectrum transceivers and terrain-following sensors.^[2] Most were mounted in a sensor array which combined several sensing devices with computers to analyze the collected data and present it to the operator.^[2] For example, ship sensors could detect cronau radiation, which all ships emitted upon entering hyperspace,^[8] which provided a few seconds' warning of a vessel approaching from hyperspace by detecting these particle traces.^[9] The larger the vessel, the more powerful the sensor array, however their large size also made them easier to detect in return.^[2]^[8] Some starships like the BTL Y-wing starfighter and utilized the stereoscopic principal to greatly enhance the accuracy of their sensors.^[7]