Dante's Peak, NASA E.L.F. (Extreme Low Frequency) Transmitter

original movie prop

This is the hero 'working' E.L.F. (Extreme Low Frequency) transmitter that the survey team removes from the 'Spider Legs' robot. Harry Dalton (Pierce Brosnan) later grabs it and takes it with him when they drive into the mine shaft so the team can locate them. This is the one from the truck in those final scenes- it has damage from the rocks that fell on it, and it also has the functioning red light. The light is controlled by a switch at the end of a long wire by someone out of camera range.
Some screen shots. The first one is just after the survey team removes it from 'Spider Legs'. The middle one is ELF on the floor of the truck covered in rocks from the mine cave in, and the final image shows the red light turned on (this still worked, I believe with the original batteries used during filming. They didn't appear to have ever been replaced...).