Montana Ghost Hunter

My friend Andy commented on my GeoPhone project and mentioned that the sensor and kit are unavailable currently.  I’ve been curious how that sensor actually works. I knew there was a magnet and it felt ‘suspended’ since moving it makes a noticeable ‘clicking’ sound.

I found this cool diagram describing how that sensor works. Looks pretty simple, I wonder how hard it would be to make.. I’m guessing the tough part is getting the right frequency.