The cat always sits at the door and meows.
Cats love freedom. When a cat feels bored or lonely at home, it will sit by the door, signaling to its owner to take it outside and play. Sometimes, a cat will pace back and forth by the door, meowing incessantly; this also indicates that the cat wants to go out and play.
Cats in heat will often sit near the door and meow if they smell the scent of a female cat nearby. At this time, owners should close all doors and windows to prevent the cat from sneaking outside to mate with other cats.
Another possibility is that cats are naturally curious, but they are also afraid of the outside world, so they sit at the door and listen to what is happening and what sounds are being made outside each day in an attempt to understand the outside world.
