While there are many different reasons that dogs bark, it is agreed upon by all that most barks are uninhibited and unnecessary. It is within your dog’s nature to bark and in most cases he will feel that he is simply doing you a favor in warning you about the boy playing on his bike outside.
Most barks are simply in reaction to a strange noise, a knock at the door, or people walking outside. While a majority of the time this can be assumed, it is important not to forget that he may in fact be trying to tell you something.
Your pup may need to go outside, or he may simply need water or food. It is also likely that he may be bored and wanting some attention or playtime. After checking that all of these needs have been satisfied, it is usually safe to assume that your dog is simply barking to hear himself bark.