The PetSafe Stubborn Dog extra Receiver Collar can be used to add another dog or as a replacement collar to the Stay and Play Wireless Containment System. The smaller, lighter, more comfortable and ergonomically designed collar features 5 levels of static correction at a higher intensity for hard-to-train pets and a tone-only mode for training. The waterproof extra receiver recharges in 2-3 hours and fits dogs 2.3 kg or more with a neck size of 15.24 cm - 58.42 cm.