Don €™t be fooled by the low aftermarket price. Perimeter Technologies is a brand you can trust with products that are loaded with exclusive features and benefits not found in the original. As a matter of fact, Perimeter Technologies' President is the same person that founded Invisible Fence brand back in 1976! nCompare Perimeter Technologies with your current R21 PATENTED Comfort Contacts cushion your dog €™s neck in soft rubber. PATENTED 3-Way, Omni-Directional antenna design eliminates the € found in lesser pet fencing systems. WATERPROOF and submersible collar receiver design. PROGRESSIVE STIMULATION allows your dog to choose the fence level that is right for their personality. ULTRA-SMALL and light weight collar design is a mere 1.1 oz! LONG LASTING replaceable lithium ion batteries. DESIGNED and MANUFACURED in the USA. Limited Lifetime warranty. 100% compatibility €“ guaranteed! nThis replacement collar receiver for 700 Series Invisible Fence systems only and will not work with 800 series or later, including Titanium Series. The Perimeter collar is not compatible with Shields Indoor Avoidance transmitters. nFULLY COMPATIBLE WITH THE FOLLOWING INVISIBLE FENCE BRAND TRANSMITTERS ICT-700, ICT-725, ICT-750, ICT-775, ICT-150, ICT-250, ICT-100, ICT-75, ICT-50, AT-950 Indoor transmitter, CT-4000 nPlease indicate 7K or 10K frequency when ordering. 7K is the most common frequency, the 10K was used in installations experiencing frequency conflicts with neighboring containment systems. Features n Replacement collar for Invisible Fence brand collarsn Collar receiver is very lightweight only 1.1 ounces n Comfortable, adjustable strap for neck sizes up to 26 inchesn Soft rubber Comfort Contacts included prevents skin irritation Item Details