[boomboomsubban]

Coins don't seem to be their target, as very few seem to be magnetic.

[toogan]

Hm, true. But I sometimes see people walking along beaches doing this kind of thing. Though they're probably hoping for rings (gold, silver, diamond, ...) rather than coins, which would make it much more lucrative as well.

[klyrs]

Gold, silver, and diamond are also non-magnetic.

[boomboomsubban]

Metal detectors, which is what they were describing, find metal that isn't magnetic.