Perimeter Technologies Invisible Fence R21 Compatible Dog Fence Collar 10K (Two Pack) Patented three antenna, omni-directional design ensures signal reception regardless of the pet's orientation to the fence These collars will only work with ICT-700 series (ICT-700, ICT-725, ICT-750) fences. Replaces Invisible Fence brand R21 Collar and includes Comfort Contacts Progressive Correction for Maximum Containment Stability PTPIR-003-10K