The Hall sensor is based on Hall Effect. It can detect whether there is a magnetic object nearby or not. And it correctly tells you through digital output.
This sensor uses the SFE Reed Switch - Magnetic Field Sensor. It can sense the magnetic materials within a detection range up to 75px.
The detection range and the strength of magnetic field are proportional.
It is useful for non-contact/waterproof type switches, position sensors, rotary/shaft encoders.
This sensor needs to be used together with an EASY plug control board. 
Features
-  Connector: Easy plug 
-  Sensing magnetic materials 
-  Detection range: up to 75px 
-  Output: Digital ON/OFF 
-  Detection range and magnetic field strength are proportional