thanx for the clipping Quisp.
Fisher Co. has often boasted of being the first metal detector makers . But that's not entirely true. They are simply the oldest in the line of *still existing* companies. There were other attempts and crude models that pre-date fisher. But those went by the way-side. As opposed to Fisher, which still exists.
Even in Fisher's own museum (which houses all sorts of vintage detectors to look at), they have a few oddities, made by others, that date back to the 1920's or whatever. I'm sure they were very crude, and could only find hub-cap sized or larger type objects.
And there was something made after WWI (1919 or so) to held find and clear out landmines from battlefields. Hence, yes, in 1929 some oddities were out there.