Sensors: Technology that detects and responds to some input from the physical environment that could include light, heat, motion, moisture, radiation, pressure, or any one of a great number of other environmental phenomena. The output is generally a signal that is converted to human-readable display or control at the sensor location or transmitted electronically over a network for reading or further processing. Sonar: Technology employing sound waves to detect and locate objects, especially submerged in water, using echolocation/reflection.