Sensor is a converter that measures a physical quantity and converts it into signal which can be read by an observer. It is the device which receives and responds to a signal when touched. It is used to measure very small changes must have very high sensitivities. Sensitivity is defined as the ratio between output signal and measured property.

 All living organisms contain biological sensors with functions similar to those of the mechanical devices. Most of these are specialized cells that are sensitive to light, motion, temperature, gravity, humidity and other physical aspects of the external and internal environment. If the sensor is not ideal, several types of deviations can be observed.