Keycharms

An item used to walk through walls, usually in a Faerie's domain home. In the walls are shaped rectangles (or archways or whatever they want to indicate the location) intended as a door, but for security's sake, these charms are often used instead of an actual knob. Anyone wearing one can walk right through, though it's regarded as polite to announce you're doing it before you do it.

Without one, the door is solid. Certain keys can be attuned to certain doors, and limited to even individual doors if the maker knows what they're doing. They must be made from gold, and they have to be held by both the owner of the door and the person receiving it to be attuned properly.
An exception to this are Guest Doors and Guest Keys. This is usually reserved for things like ballrooms for more affluent people, where the doors can be walked through by anyone with a key without any attunement to the person holding it.

Poorer-but-wants-to-be-fancy faeries do this around the house in most rooms that aren't strictly private (bedroom, Master Bath, dungeons, etc.), as the process is cheaper, more accessible, and easier to handle, because you can always just hand your guest one of the few keys there are, and you're not likely to have a stray key nor are you likely to have an unchecked guest.

They actually work by wrapping the wearer in a field of magic that responds to the make of the door and moves the loose particles out of the way. It's only a little field and people swear they feel the door touching them because as far as they can tell, it does, that's how close the field is. It's closer to them than their armhairs.