I don’t know if most rats enter the home through the front door. I would guess that is pretty rare. Unsealed crawl spaces and attics are much more likely to be the culprit.

Even then, they don’t necessarily do any harm. As long as the interior of the home is sealed, they can’t get in. Our building definitely has rats, and we saw one in our home shortly after we rented it. The previous tenants had just trapped rats they saw, but we insisted that the landlord send someone to seal every ingress point (with copper wool and silicone gel). Since then we haven’t had an issue, even though our little visitor would come daily before.

As a bonus, the same way rats get in, so do cockroaches. In NYC, older buildings, especially near the ground floor, are notorious for cockroach infestations. But we don’t have any of those in our unit either, despite the building being a century old. Turns out cockroaches and rats aren’t made of magic. They can’t teleport through solid material. If the interior of your home is sealed, they cannot get in.