Analog Linear Hall magnetic module
This module comes in two versions, the digital version (available here) needs to be plugged into a digital pin and the analog version in an analog pin of your microcontroller.
This product reacts when they come in contact with magnets. An example use can be as a door open/close sensor if you have a sensor on the door frame and a magnet on the door. This unit will pick up when the door is open or close. They are often used on wheels etc. to count the times or the speed of wheel rotation.
Analog Linear Hall magnetic module spec
Operating Volts: 5V
+ 5V, – Gnd, S-signal