The perfect key for your cat is this e-Sensor collar!
The ideal Electromagnetic E-Cat™ Door is sold separately - uses this collar to ensure that only your pet has access to the cat door. You can replace a lost collar or allow additional pets to have access to the E-Cat™ Door. This collar is designed for safety and security that controls the door ensuring that no other critters - or burglars - enter your home. The Extra Collar includes a 9-volt battery.

Dimensions: 4"L x 2.5"W x 2.5"H