Hey! You dropped your hat kid...
hey! Leave it alone
Hey!
Hey is to call attention alright. However when speaking or texting an adult specially an older person, your boss, your mother in law, your own mother or father, I feel it should be after you have said a proper greeting. Hello, hey do you know when will the children come from vacation? Better yet skip the hey all together. Personally I see it as a sign of ignorance.