There are several types of bark that dogs use to communicate with people. Most dogs learn at a young age to bark when they need to go outside, want to come indoors, or to remind us that it is dinner time. Dogs have a specific bark to let us know that something is suspicious and needs attention.
Dogs do not bark without reason. Like humans, dogs are extremely social creatures and most dogs hate being left alone outside while their family is indoors. Dogs that are left outdoors for extended periods of time become bored, or they become anxious about being alone. These dogs tend to bark at every sound or movement in the neighborhood because they feel vulnerable when by themselves, especially if they are tethered.