Got a feeling it was a Swedish guy who developed the Goldspear but they were sold from Beaconsfield in England from 1990/91.
There were several 'kits'
Goldspear Prospector. Would instantly record any minerals and seperately indicate any gold partical down to 300 Mesh (0.002").
Supplied with a 4 foot probe plus a four foot extension.
The GP2, same as above but with 2 foot probe and 2 foot extension.
Goldspear Mk 2. 50% more sensitive locating particles down to 400 mesh. 4 foot probe and extension. Instead of headphones you got a loudspeaker with adjustable amplifier and a rechargable kit.
Mark 2 GM2. As the Mk 2 above but with 2 foot probe and 2 foot extension.
From what I remember (and I haven't seen one since the early nineties) it had audio warning and three lights (red,green,amber). Think one light indicated some gold but not enough to warranty recovery while another indicated that there was enough gold to be worthwhile panning.
It worked but I think the reason you don't see them around was false indications I assume from black sand or similar. Also they were expensive with the Mk 2 being