SureFlap Pack of Two RFID Collar Tags Compatible with the SureFlap Microchip Pet Door, Cat Door, DualScan Cat Door, SureFeed Microchip Pet Feeder (*serial numbers higher than 1152201 on the Cat Door) For use with non-microchipped pets Each collar tag has a unique code and weighs just 2g Collar tag diameter: 1" Each pack contains two collar tags