What is the X in X-mas?
sensor sen·sor (sěn'sər, -sôr')
A device, such as a photoelectric cell, that receives and responds to a signal or stimulus.
See sense organ.
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.