Worse than nothing - DO NOT BUY!!!
If you have female, unneutered cats, DO NOT BUY this product!
It is staggeringly badly designed, in so far as it is impossible to set it to "entry only". If ALL your cats are not microchipped, they will be trapped outside, and subsequently impreganted by feral toms.
In addition, its lock mode is easy for the cats to bypass - my cats figure out how to get round it within a few weeks. Also, no low battery alert to tell you the batteries are running low.
I wish I had never touched it-Disgusted