Electrical metal tester?

I saw a device the other day, hooked up to 2 aligator clamps with an
electronic meter that read metal content for gold silver or whatever.
the screen read out what karat the gold was, the device itself was
about palm size may be slightly larger, where can I get one what are
they called and do you only need one for all metals? I have people
who trying to encourage me give mom old broken stuff saying they dont
know if its real but I can have it if i can melt it and use it.

It is a GLX-24 Pro gold tester from Tri Electronics, which can be
purchased from almost any jewelry supply company. (Stuller, A&A
Supply, Rio Grande)… There not cheap, I have one, they are great.