Sensors detect physical changes in the device’s environment and output them as analog voltages or digital signals. This is then sent to a human-readable display where it can be monitored, transmitted, or relayed to other electronic devices for further processing.
An electronic sensor is usually equipped in a way to be able to pick up the slightest changes in its surroundings and instantaneously relay the information for processing. The higher the sensitivity of the sensor, the better it is.