Sound is the giveaway for house and field crickets. A male calls by rubbing his wings together, and the chirp seems to come from everywhere at once, which is why people spend an hour pulling out the stove and never find him. Chirping that lasts more than a few nights, or comes from more than one room, means you probably have more than one.
Camel crickets don't chirp, so the signs are visual. You find them clustered on basement walls, in the corner behind the oil tank, in the sump pit or stuck in the tub of a utility sink. Turn on the light in a damp unfinished basement and watch the floor, and you will know quickly. Glue boards set along the walls overnight are a good way to gauge how many there are.
Damage is the other clue. Crickets will chew on cotton, wool, silk and synthetic fabrics, especially items stained with sweat or food, plus paper and cardboard. Small irregular holes in clothes stored in a damp basement, or chewed edges on boxes, can point to crickets. If the holes are in wool stored upstairs, see our clothes moth page instead.