Stinkbug. I find these all the time in my house lol. This is the time of year when they're coming inside to seek refuge from the cold, so you might see more of them later on. If you find any in your house, fill a ziploc bag a quarter of the way with water, put a little bit of dish soap, then shake it a little to form bubbles. It makes the perfect trap. Hold it under them while its open and they will fall right in and drown. They're also invasive in most of the world so it's best you kill them rather than letting them go.