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

https://cesarrufv010.wpsuo.com/why-you-need-to-clean-your-crawl-space-right-now-1

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