This whistle creates high decibel intense tones around the 8kHz range, known as "the middle zone of best hearing sensitivity for dogs." The Pat Burns PB-100 "Green Monster" Whistle was developed by Merry Lake and Pat Burns in 2005 in response to the increasing difficulty of stopping dogs on field trial blinds. This whistle was developed and tested in a sound laboratory, resulting in the special shape which projects the sound in a concentrated cone directly at your dog. The acrylic construction adds durability and virtually eliminates sonic distortion. The dark green color was chosen so that the PB-100 Green Monster Whistle could be used by hunters and hunt test competitors as well as field trialers.