Can other cats who have been chipped get in?

Only the cats that you programme into your cat flap can get in. You don't have to know the microchip numbers either. 

Just hold down the green button for 10 seconds until it beeps, then pass your cat under the porch sensor (like scanning an item at the supermarket!) the cat flap will then beep three times and your cat is programmed in. 

Switch it off at the mains then on again to reset it and the cat flap will then lock and only unlock for your cats.

You can repeat the process as many times as you wish to programme all your cats in. The cat flap will remember up to 31 cats!

Another method is to put the cat flap into programming mode and then push your cat out through the cat flap (don't force him!) then it will beep three times to let you know your cat is programmed in. Then reset the cat flap (turn it off then on again) and tempt your cat back inside with their favorite treats!