3M EMS Extended Range Ball Marker is specially designed for locating flush mounted facilities that are covered by backfill. It is affixed to the underside of non metallic lids or covers over flush mounted facilities. This self align marker offers positive identification of facilities. 3M EMS Extended Range Ball Marker provides an effective way of marking underground facility lines.This passive underground marker with a water resistant polyethylene shell does not react with any chemicals or minerals. This ball marker effectively operates without the need for any external power source.