Mice in a crawl space may reveal themselves through scratching sounds at night, droppings, chewed openings

https://reidtmmg514.urbanvellum.com/posts/how-rodents-sneak-into-san-diego-rooflines-3

Mice in a crawl space may reveal themselves through scratching sounds at night, droppings, chewed openings, nesting material, or even unusual pet attention.