The Tri-Tronics Field 90 G2 is an electronic dog trainer that is commonly used for basic obedience as well as by trainers who need both momentary and continuous stimulation. Has 6 continuous stimulation levels and 6 momentary levels, with a 1 mile range, audible tone and is designed for use with only 1-dog. For the same series that is expandable for up to 3 dogs see the Tri-Tronics Field 90 G2 EXP. (Additional EXP Receiver collars are required to expand the Field 90 G2 EXP model).