The phrase “Are you in?” can have several meanings, depending on the situation. To ask if someone is joining or participating Example: “We’re going to the park later. Are you in?” Meaning: “Do you want to join us?” or “Do you agree to take part?” To ask if someone is at home, at work, or inside a place Example: “Is your brother in?” Meaning: “Is your brother at home?” So, by itself, “Are you in?” most often means “Do you want to join?” but in some cases it can also mean “Are you here?” depending on context.