Everything you need for a 3-Cat Household. A combination of three Transmitter and Receiver Tags - read below Three silicone collars of your choice Attachment hardware Each AGGRESSIVE cat wears a black Receiver Tag, and each PASSIVE cat wears a gray Transmitter Tag. When the AGGRESSIVE cat gets too close to the PASSIVE cat, the Receive Tag will vibrate and buzz. *If you have TWO aggressive cats and ONE passive cat, configure order for two Receiver Tags and one Transmitter Tag. *If you have ONE aggressive cat and TWO passive cats, configure order for one Receiver Tag and two Transmitter Tags. Please Give It Time Changing a cat's behavior takes time. Please don't expect PEACE PAWZ Tags to immediately remedy what has likely been part of a cat's personality for years. Please be patient and give your cat a chance to learn. We promise, it's worth it!