The police come to your door and knock. They announce themselves. It's the middle of the day. Even so, something just feels off about the encounter. You have no idea why they're there. Do you have to let them in?
You don't. You don't even have to open the door. Some experts advise just talking to them with the door closed. The police officers are merely strangers knocking on the door. Would you open it and let just anyone into your home? Their uniforms do not change anything. Politely tell them that you would rather they didn't come in and they have to do as you ask.
Now, they can come in if they have warrant or just cause, in some cases, to think you're in the process of committing a crime. So, if they're insistent, just ask to see the warrant. If they can't produce one, it means they probably don't have enough of a reason for the court to give them one. That definitely means they don't have enough of a legal reason to enter your home. Ask them to get a warrant and come back, emphasizing that you're happy to cooperate if they follow the right procedures.
Much of the time, officers who knock without a warrant are just fishing for something. They're hoping you accidentally incriminate yourself or they're trying to find some excuse to arrest you. Don't let the uniforms fool you. You don't have to do it.
If you do get arrested, especially if they force their way in without a warrant, make sure you know what defense options you have.