This is my third Pet Porte Cat flap and I have always found it to be an excellent product. It works by recognising your cat's microchip so no need for collars and all the disadvantages and dangers that brings and all other cats are excluded from entering your house. The cat flap has several different settings for use i.e. if you want to keep your cat in overnight it will recognise falling light levels and lock until the morning when it will unlock again. The service from CatFlaps.co.uk was fast, the product was well packaged and I found the web site easy to use.