Knock, knock

When coming to a person's house or a small shop, it's habit to call "Inside!" to get the people's attention. "Inside, inside!" If you wanna be a jokester, you might respond "Outside!" to signify you've heard the summons.

Alternate form of getting a home's attention: clapping. No verbal greeting, just clapping. At a clap, you're expected to come running to see what's up.