Access through the door is controlled by a magnetic locking mechanism. The collar tag is approximately the size of a pea and is worn on the pet's existing collar. While the PetSafe Magnetic Cat Flap will keep feral cats from entering your home, it will not prevent "inside" cats from using the door to go outside. The 4-way locking mechanism allows you to control the access of your cat by manually setting it in one of four modes.
The flap on this cat door is made with a rigid plastic and has a magnetic strip along the bottom to hold it in the closed position. This door comes with a three year manufacturer's warranty. Installation Note: This magnetically triggered door may not perform if installed into steel or doors that have magnetic materials. Most residential doors are aluminum / insulated. Aluminum is non-magnetic so this should present any problems.
If you want to double check to see if the surface this is being mounted in is magnetic, simply hold a magnetic close to see if there is any attraction.