sensor

n. device that responds to physical stimuli; bodily organ that receives sensory stimuli, sensory organ

A sensor is a type of transducer. Direct-indicating sensors, for example, a mercury thermometer, are human-readable. Other sensors, such as a thermocouple, only produce an output voltage or other electrical output which must be interpreted by another device (such as a computer). Most sensors are electrical or electronic, although other types exist.
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Sen·sor n. 1. A device, such as a photoelectric cell, that receives and responds to a signal or stimulus. 2. See sense organ. [more]Sensor - Community and Resources

Noun
1. any device that receives a signal or stimulus (as heat or pressure or light or motion etc.) and responds to it in a distinctive manner
(synonym) detector, sensing element
(hypernym) device
(hyponym) metal detector
(derivation) feel, sense

n. sensor, device that responds to physical stimuli, bodily organ that receives sensory stimuli, sensory organ