The difference between Scruggs and Keith de-tuners is that Scruggs devised rather crude cams on pivots on the peg head, which pushed and released tension on the 2nd and 3rd strings (allowing quick change from open G to open D tuning). Keith refined the process, by designing a peg with internal locks that did the same thing more accurately, and without cluttering or adulterating the instrument’s headstock, plus allowing for the differences between the two strings (b down to a, and g down just a half tone to f#). Of course, the high g string has to be adjusted separately, or just avoided, because you end up with gDF#AD when dropping from gDGBD, so these pegs arguably are more useful to bluegrass players than old timey frailers.

Scruggs famously used his de-tuners on instrumentals such as Earl’s Breakdown (just 2nd string b to a), Flint Hill Special, Foggy Mountain Chimes and Randy Lynn Rag (2nd raising from b to c). Keith famously used his pegs on all four strings to play Auld Lang Syne, without fingering any frets. Guitarists have had similar gizmos, from the tremolo arm on Fender Strats, to Gene Parsons’s internal string bender, and more recently Hotshot tuners, which similarly can be used both for quick re-tuning between songs or for fancy effects whilst actually playing, though many prefer to just use light strings and bend them up a tone or two, willing them back to pitch with strained facial contortions (presumably just in case it doesn’t quite work out?).