Another very intriguing build, this time by user dc1rdb, who described some of the build detail on GitHub: Rock hunting · OpenGammaProject/Mini-SiD · Discussion #9 · GitHub

It's a mini SiD connected to a microcontroller that works like a voltage controlled oscillator with a buzzer! It'll change it's output tone frequency with the measured activity. There is a really cool video on GitHub (link above), that I can't really show you here, where he demonstrates the device packaged in a tube with a 3D printed handle. The samples he has collected here are pretty impressive, especially since he's got no problem detecting the rocks already from a couple of meters away.

Let me know what you think about this one :)

Cheers!