Although it may seem like your dog is afraid of the doorbell, he's likely nervous about what will happen after the bell rings. Dogs make associations between stimuli — the jingling of car keys signals that their owners are leaving, and the sight of a leash means a walk is about to take place. In the same way, your dog connects the sound of a doorbell with events that typically occur afterward, such as new people invading his territory.
To determine if your dog is apprehensive when it comes to visitors, watch his reaction after you open the door. If he barks but then greets the person with a loose tail wag and relaxed body posture — including a relaxed mouth, ears and eyes — then fear is likely not an issue. But if it takes him awhile to warm up to a certain person or if his body stiffens, then he could be reacting out of fear.
During training consults, I often visit the person’s home so I can assess a dog’s confidence level around people, as well as gauge how the dog interacts in his own environment. Some dogs show discomfort with more blatant body language, such as growling or cowering, while other dogs display very subtle signs, like standing behind their owners. With dogs who are riled by doorbell ringing or door knocking, I work to turn the dog’s underlying fear or discomfort into a more positive experience.
One of the best ways to do this is to leave a jar of treats outside your door, so people can toss them on the ground when they enter. I instruct visitors to ignore the dog by looking away and keeping their bodies turned slightly to the side. I then ask them to gently throw treats a few feet from the dog, so he has to move to get the snack. This process turns the fearful event of greeting someone into a situation the dog can control.
Most importantly, visitors should give the dog attention only once he has shown signs he's willing to approach and greet them. When a person makes the first move toward a fearful dog, it immediately puts the dog in a defensive mode, only confirming the negative association he has with people. Some dogs can even react with aggression, which can be an outward expression of fear. If your dog shows any type of aggression or extreme fear, it’s best to consult with your veterinarian.