Likely clover mite

Often found on exterior walls and around windows, then indoors near lawns, gardens, or other vegetation.

Pierces plant cells and feeds on grasses, clover, and other plants; it does not feed on people or pets.

Tiny reddish mites may wander indoors, especially in spring and fall. When crushed, they can leave red stains; the photo’s red specks alone cannot confirm this identification.

Harmless to people and buildings, though occasional plant feeding and indoor nuisance are possible. September activity in the United States is plausible, but the country-level location is too broad to verify range.