Amazon.com: SportDOG Brand SportHunter 1225X/1825X Add-A-Dog Collar - Additional, Replacement, or Extra Collar for Your Remote Trainer - Waterproof and Rechargeable with Tone, Vibration, and Shock : Pet Supplies
Amazon.com: PetSafe Add-A-Dog Remote Training Collar – Perfect for Small, Medium and Large Dogs – Choose from Tone, Vibration, or 15 Levels of Static Stimulation – Waterproof and Durable – Rechargeable : Pet Supplies
PetSafe Yard & Park Add-A-Dog Receiver Training Collar - Walmart.com
Premier Pet In-ground Adjustable Add-a-dog Collar - Black : Target