The Cat Mate Elite uses the latest in R.F.I.D. technology and offers major advancements in pet access control. Entry and exit is operated by unique electronic Collar I.D. Discs (2 supplied) for up to 7 cats - keeps all other animals out. The Cat flap has a secure 4 way locking system. Only animals with a RFID collar tag programmed into the door can exit or enter the door. 4 AA Batteries (6 to 9 months) not included. Self-lining to 2” (50mm) - suitable for single/double glazing, doors and panels, including metal. Wall Liner available for wall installation (not included). NOTE:Please refer to the instruction manual on how the door must be installed in metal door to function properly.