It is an old school traction devise , used in the 50's and 60's mostly on Police cars and emergency vehicles. I'ts a mechanical devise with a heavy weight ( 60lbs ) suspended on springs. Apparently the inertia from the car sliding one way, sends the weight the other way to counteract the slide. Don't know if it really works or not. I might put it back in after I do the trunk area. It is heavy though, I am curious as to its performance.