I got asked yesterday if I wore a special collar to let me into the cat door. Unfortunately no. The reasons are that when I did wear a collar, I was losing one a week in the garden or around the house and I was constantly kicking it off.
There are cat doors that only let your cat in when it is wearing a collar with a special magnet in it. One of our friends had that kind, but cos her cat kept losing their collars, it was very expensive to use as the magnets were costly to buy.
We have heard that there are new cat doors that know your cats micro chip and only lets your own cat through, which sounds like a better option, although because they are new, they are very pricey to buy here.
In NZ we don't have any critters in the neighbourhood who sneak in. Mum does think that a couple of local cats do try and sneak in and eat my left over jellimeats.
The cat door is super handy and gives me access to the garden whenever I like to come and go.