This is an extremely rare Pat Flanagan Experimental Sensor III. It has a Ruby Gem in the center of the front. Info on this item can be found at /sensor.html . This particular design can be found about a quarter of the way down the page right above a picture of Pat Flanagan. T are no more being made and none are available so this item is very rare. T is no chain for it. If you have any questions just send me a message. The letters on the left side are a little worn but you can still make out what it says. "1979 Pat Flanagan experimental SENSOR lll made in USA. Other than that, it is in pretty good shape. The picture is not of my item cause I could not get a good shot. The numbers on top read 12155.