Mittens is a neighbor's cat. He spends most of his time outdoors. We have the key to the neighbor's house. Occasionally, when we are certain that they are not home, we open their door to let Mittens in. And several times a year when they are away, we take care of Mittens and their 2 dogs.
So Mittens knows us and whenever he wants to go inside his house, he comes to our porch and starts waiting. From there he can also spot his owners' cars turning the corner and go after them to be let in.
Ironically, however, Mittens often gets stranded outside when his owners are home, because they don't check up on him and, we wouldn't, of course, just unlock their door from the outside to let their cat in.
We've found Mittens on our porch wet and cold more than once. We now keep an old towel ("Mitten's towel") on the porch with which to dry him. He frequently sits on our old rocking chair and occasionally, perhaps when he is really cold, lets me put the towel around him. Last Monday nite was one of those occasions.
One interesting thing about Mittens is that he recognizes me as a friend only in the front of my house. A few times when he encountered me in the backyard he quickly turned around and ran away even when I was calling out his name.