These tags will work with the Sureflap cats flaps or Surefeed feeders. Ideal for cats/dogs that are not microchipped. Improves flap/feeder reliability in cases where the pet chip doesn't read well. The SureFlap and Surefeed Key works with both the Sureflap and the SureFeedand can be used for an additional pet using them or as a replacement if your pet's SureFlap Key is lost. Worn on your pet's collar, the Key uses radio-frequency identification (RFID) technology by using a unique code to signal the Passport to operate as programmed for your pet. The Key is about the size of a quarter and does not require batteries to operate. Program up to 20 Keys to your Sureflap Door Split. Key rings included to easily attach to pet's collar. No batteries needed. Simply attach to your cats collar and they're good to go. The SureFlap tags are used to operate the rfid/microchip cat flaps so that only the cat wearing the tag can enter or exit the house. Each collar tag has a unique code and weighs just 2g Dimensions: 35 x 24 x 5 mm Water-resistant Compatible with theSureFlap cat door and Surefeed feeders Package contains: 2x SureFlap and Surefeed compatible RFID tags