How do auto locking hubs work?

Normally both wheels on a single axel revolve at an identical rate. Vehicles with auto-locking hubs have sensors that monitor the speed of each wheel independently. If a speed differential is detected meaning if one wheel begins to spin faster or slower than the other wheel, a solonoid (switch) is activated releasing the hubs such that they can spin in and lock. Because only one wheel has torque at any time, if there is a differential speed between the 2 wheels, it means that the torque wheel has broken loose.