A Hall-effect sensor is a transducer that varies its output voltage in response to changes in a magnetic field. Hall sensors are used for proximity switching, positioning, speed detection and current-sensing applications. In principle, they are analog but can be used to operate digitally by a Schmitt trigger output. These sensors are very common, small and inexpensive; they also have the advantages of being insensitive to dust, humidity, vibration, etc. Hall-effect sensors exhibit constant-over-time behavior.