Have you ever wondered how your dog knows it's you coming home after a long day at work, or an evening out? How does she know, as you come through the door, that you're not some scary stranger invading her territory?
It could be she hears familiar "coming home" sounds, like the garage door opening as you pull into the driveway. Maybe she recognizes the hum of your car's engine, or your footsteps approaching. Maybe she catches a whiff of your personal scent as you open the door.