Spiders often sneak in from outside. Trim bushes away from your house, and sweep away webs on porches and eaves. Install yellow bug lights—they attract fewer insects, which means less spider interest.
You can also sprinkle diatomaceous earth (a natural powder) around door thresholds. It’s non-toxic to pets and people, but deadly to spider exoskeletons. Think of it as a gentle moat they’d rather not cross.