This is the SportDOG Sport Hunter 1825 Add-A-Dog Extra Collar - an extra collar for the SportDOG SD 1825 System ithat ncludes a 3/4 inch collar strap that fits up to a 23 inch neck, charger, short and long contact points, and charging cradle. The collar features an ergonomic slim-profile collar design ensures a perfect fit and has all the built-in performance you need to control a second hunting dog using a SportHunter transmitter. This receiver has up to one mile of range. The waterproof DryTek receiver is submersible down to 25 feet. It uses rechargeable, replaceable lithium-ion batteries and has a low-battery indicator. It has a 40-60 hour battery life and fully charges in just two hours. On and off switch on receiver.