Dimensions: 25 x 24 x 5 mm Water resistant. Compatible with SureFlap cat doors and Surefeed feeders. Package contents: 2 x PetSafe SureFlap and Surefeed compatible RFID tags. Compatible with SureFlap Microchip pet doors, cat doors, DualScan cat doors, and SureFeed Microchip pet feeders. Multi-pet home – Ideal for homes with multiple cats. Microchip cat flaps can be used with a number of key fobs, allowing only your cat to enter. Independent – Microchip cat flap for your pet. The key fob allows your cat to come and go as they please, without the need for owner supervision. Cat-resistant - The resilient and durable design of the Microchip key fob can withstand even the most active cats. The lightweight and water-resistant design makes it virtually imperceptible to your cat. These tags are compatible with Sureflap cat flaps or Surefeed feeders. Ideal for missing cats/dogs. Improves the reliability of the flap/feeder if the pet chip is difficult to read. SureFlap and SureFeed keys work with both SureFlap and SureFeed and can be used for additional pets or as a replacement if you lose your pet's SureFlap key. The keys are attached to your pet's collar and use RFID (Radio Frequency Identification) technology to use a unique code to signal the passport to function as programmed for your pet. The keys are about the size of a quarter and require no batteries. Up to 20 keys can be programmed into a Sureflap door split. Keychain that easily attaches to the collar. No batteries required. Just attach it to your cat's collar and it's ready to use. SureFlap tags are used to operate RFID/microchip cat flaps, allowing only cats wearing the sign to enter and exit the house. Each collar tag has a unique code and weighs only 2g.