MineLab E-Trac, MineLab Safari, MineLab Explorer XS,
White's 5000 D, White's 6DB, White's 5000 D GEB
Sunray X-1 for the ML's, Garrett PP for the White's and a Backhoe
If I remember, it limits the volume when you pass over an "overload" target, so as not to blast your ears off. I own two different types of Greyghost, and I do like them.