This extra SmartKey™ Electronic Key, can be used for additional pets using your SmartDoor™ Electronic Pet Door. Our innovative SmartDoor™ Electronic Pet Door recognises the SmartKey™ Electronic Key worn on your pet’s collar and unlocks the pet door. When the SmartDoor™ Electronic Pet Door no longer senses your pet's SmartKey™ Electronic Key, the flap automatically locks back into place. The SmartDoor™ Electronic Pet Door can detect up to five programmed SmartKey™ Electronic Keys. WARNING Small children can pass through the door. Read entire statement.Features Additional SmartKeyâ„¢ Electronic Key for the SmartDoorâ„¢ Electronic Pet Door Program up to 5 SmartKeyâ„¢ Electronic Key units Waterproof collar submersible up to 1.5 metres Compatible with the SmartDoorâ„¢ Electronic Pet Door