know this TWOBOX Detector ?

[TOYO]

sound like a pulse detector

https://www.youtube.com/watch?v=LGw7xn9I0Xs

[Tim]

Hmmm...She's a beauty. I have a Garrett Bloodhound DM5 for my ADS, but that thing blows it away! I suppose the sound is generated through a 555. Clip says vlf. That is all I can say to help identify the circuit. Maybe try contacting the maker, and report back here Toyo?
I hope you have a mini backhoe if you intend to use that.