sensor

from WordNet (r) 3.0 (2006)

sensor
    n 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 [syn: {detector}, {sensor}, {sensing
         element}]

from The Collaborative International Dictionary of English v.0.48

Sensor \Sen"sor\, a.
   Sensory; as, the sensor nerves.
   [1913 Webster]

from The Free On-line Dictionary of Computing (8 July 2008)

sensor

   <hardware> An electronic device used to measure a physical
   quantity such as temperature, pressure or loudness and convert
   it into an electronic signal of some kind (e.g a voltage).
   Sensors are normally components of some larger electronic
   system such as a computer control and/or measurement system.

   Analog sensors most often produce a voltage proportional to
   the measured quantity.  The signal must be converted to
   digital form with a {ADC} before the CPU can process it.

   Digital sensors most often use serial communication such as
   {EIA-232} to return information directly to the controller or
   computer through a {serial port}.

   (1997-04-15)