A Hall Sensor is a non-contact device used to measure a magnetic field. It works by detecting changes in the magnetic field around it. They are commonly used for position sensing, current sensing, speed sensing, and sensing magnetic fields in a variety of applications. Seeed Studio produces a Hall Sensor, compatible with Arduino and other popular Single Board Computers. It uses an integrated Hall Effect switch to accurately measure magnetism, and an A3144 Hall Element chip to output an analog voltage, which can be used to interpret and control the measured magnetism. It is ideal for motion control, speed sensing, and proximity sensing.