@hmdjobs: Long before electronic backup beepers became standard on commercial trucks and construction equipment, drivers relied on clever mechanical bells like the Warn alarm. Mounted directly to the center of the wheel hub, this self-contained unit contains four weighted steel balls resting in guided channels. When backing up, gravity causes a ball to drop and strike the bell every ninety degrees. As soon as the truck drives forward, centrifugal force slings the balls into side pockets, silencing the alarm completely.   Big thanks to @VOLKSWAGNUT for sharing and demonstrating this incredible piece of vintage trucking history! Check out the full original demonstration video: https://www.youtube.com/watch?v=0MbRmTuolm8   Drop a comment below: would you prefer this reliable mechanical bell over modern electric beepers?   #hmdtrucking