SureFlap CatFlap uses the radio frequency from the microchip already embedded in your cat (or small dog) to keep furry squatters out. The clear plastic door is unlocked when the sensor reads your pet’s microchip. The SureFlap, which in the past only worked in Europe, can now read U.S. 10-digit microchip frequencies. Up to 32 microchips can be memorized by the door, though we hope you aren't hoarding over two dozen felines in your home... The flap can even be installed within a wall, which could be super beneficial if your cats eat different foods and one is a grazer while the other is a Hoover vacuum. You could set this up so only your grazer has access to a room where their special food is in. Just beware that microchips get harder to read by sensors the more your pet gains weight. To ensure that your cat doesn't ever get locked out, and lives a healthy life, keep 'em lean and mean.