Not the cheapest, but recommended as entirely reliable and trouble free. Get your feline friend chipped if he / she is a roaming ex-farm cat like ours. Batteries have been in nearly a year now and still working well. No loud clicks, or noisy flap if your cat is easily spooked. Got the new kitchen door fitter to cut the hole in the PVC door and fit it, well worth it rather than DIY for such a great product. Clear plastic door gives the cat every opportunity to look out or in, and the switch only trips when his head comes into contact with the door, hence the batteries last well. Wipe clean plastic all round so always looks good on a white door. A top class product.