These are in fact pneumatically operated tire chains. Quite ingenious might I add; a dash-mounted switch activates a pneumatic (a compressor is needed if your truck does not have air brakes) solenoid, which engages a disc that rotates off the tire. That disc has chains attached to it which go under the tire providing instant grip. Watch the video.
Originally invented by a Swedish milk delivery man named Göran Torneback, the idea was later refined and patented by American inventor W.H. Putnam. The automatic tire chains were designed to add low-speed traction on ice and up to six inches of snow. For deeper snow, conventional chains should still be used.
The instant automatic chains have applications for half-ton trucks or bigger, mostly due to tire size and ground clearance. There are two manufacturers, American Onspot (great for Military or Government) and German RUD. Both work in the same way but probably have different vehicle applications. Onspot units cost $1500 or $1800 if your vehicles needs a compressor. Allow six to eight hours for installation.
I have never heard of this until my friend Mike sent a link to the video. Pretty cool, needless to say I now want to get an half-ton pick up truck (or perhaps the Ford Raptor?) and move to Maine. Since I live near a hospital and a fire station, when an opportunity arises I will ask a fireman or a EMS person for opinion on these tire chains.