Sensors

One of the prime security measures is the use of sensors, devices able to pick up and monitor certain types of information, sending out an alarm or activating other security measures when they detect intruders.

Sensor technology in the 24th century is capable of picking up nearly every type of energy in the electromagnetic spectrum (and some exotic energies outside of it), along with biological matter, and even specific DNA sequences.

Most sensor packages consist of multiple types of sensors, each detecting something different. For example, a sensor suite might scan for electromagnetic disturbances, ionization traces (indicative of a transporter beam), infrared signatures for body heat and working machinery, and so forth.

Visual Sensors

Visual sensors transmit a visual image of the area they are set to scan, similar to old-fashioned security cameras. They can be crudely overcome by blacking them out with some opaque material (paint, for example). A more sophisticated option is to install a device that feeds the sensor's data back into it, creating a "loop" and effectively blinding the sensor.

Motion Sensors

Motion sensors detect molecular displacement traces created by moving objects. The sensors generally have a "threshold" of movement they are designed to detect. If the threshold is set too low, the random movement of air molecules can be enough to set the sensors off. Low-grade motion sensors can be evaded by moving very slowly. Otherwise, its easiest to defeat motion sensors by overcoming the computer that controls them.

Infrared Sensors

Infrared (or IR) sensors pick up infrared radiation or heat sources, including the body heat of warm-blooded lifeforms. Characters can overcome them by wearing special anti-IR clothing to masks their heat signature, or by programming a device like a tricorder to emit an IR scattering field.

Electromagnetic Sensors

These sensors detect electromagnetic disturbances of various kinds, including the operation of certain devices, the use of energy weapons like phasers, and so forth. They can be avoided by not using any high-energy devices, although this can make overcoming other sensors more difficult. Characters can also use technology to shield electromagnetic impulses, preventing them from being picked up by the sensors.

Subspace Sensors

These sensors are fairly rare, they detect disturbances in the subspace field, such as those caused by warp nacelles or a transporter beam. They can detect anyone beaming in or out of an area, and provide information to help track the transporter beam's source.

Starship Sensors

Starships rely heavily on the data provided by their various sensors for tactical and navigational decisions. Without its sensors, a ship is effectively blind and deaf, unable to detect anything except by having someone go to a window and look out. Therefore, many tactics in starship combat are based on fooling or shutting down an opponent's sensor systems