How can I get my longhair Chihuahua to stop barking?

He is about a year and a half old. He is very loving to most everyone. He loves everyone in my family and in my boyfriend's family. But whenever someone walks by our door he barks non stop. Or if there we are outside he will try to run after them barking. He grumbles and growls if they don't come over to him. We have tried using Bark Off and that doesn't work. He changes his barks so it doesn't go off. We would just like to get him to stop barking at people walking by and other noises.