The Tri-Tronics Pro 100 G2 dog trainer is designed for beginner as well as advanced training that may include obedience training, retriever training police and K-9 work as well as Schutzhund training. The unit has 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 Pro 100 G2 EXP. Additional EXP Receiver collars are required.