I found some INSIDE my car...
You'd be surprised how they can get into your house. I was in my attic and found sunflower seed shells up there.
One evening I had my sister and brother-in-law over for a small summer bar-b-que on my back deck and while seated at the table, I saw a mouse actually scamper up the bricks of the chimney and enter a small crack into the roof between the flashing and the chimney bricks........
Squirrels can climb brick walls too but that's another story........