A Hall effect sensor can measure the distance from one point to another. A real world application can be found in 3D Printing for DIY enthusiasts. One of the biggest problems with 3D Printing is levelling the bed before printing. To simplify the task, a Hall Sensor can be attached to the extruder. The sensor measures the distance from the extruder to the bed without the user having the constantly adjust the printer's bed after each print.
Indium Arsenide wafers are used in mid-infrared Light Emmitting Diods (LEDs) and detectors, see above, and InAs large Hall Coefficient makes a great magnetic field sensor.