What is a knock and talk?

It's an investigative technique built on a legal premise: officers may approach a home and knock, the way any member of the public might, without needing any suspicion at all.

What makes it effective is that most people open the door, and most people talk. From there, everything the officer sees or smells from a lawful vantage point becomes available, and any consent given becomes a basis to enter.

Where it exceeds its limits: officers who go around back, who enter fenced areas, who bring a dog to the door, who knock at hours no ordinary visitor would, or who refuse to leave when asked. The implied permission a visitor has is limited, and conduct beyond it can turn the approach into a search.

You are not required to open the door, not required to answer, and not required to step outside. Stepping outside is a common and consequential move — it removes the doorway protection without gaining anything.