Innotek Extra Receiver, SD-3000/SD-3100 SYSTEMS Extra receiver for SD-3000 and SD-3100 Contain-N-Train Systems. the collars are compatible with Innotek Fencing Systems Contact probes; test light; replaceable 3-volt lithium battery Water-resistant design; lightweight at only 2-2/7 ounces for comfort Nylon collar strap fits neck sizes 8 to 21 inches Measures 3-1/2 by 3/4 by 1-3/4 inches; limited lifetime warranty