If police come to your door and you don’t need their help, you can simply decline to answer. They cannot come into your home without a search warrant.
Even if the police have probable cause, they cannot come in your home without a search warrant.
You might even be a suspect in a criminal investigation. In such a case you should remain silent — except to say:
“Officer, I cannot let you inside without a search warrant.”
Following such an encounter, you should immediately contact a lawyer before speaking to police again.
The fact is that police can legally lie to try and gain access into your home and knowing how to deal with police at your door can go a long way.