Well I have two basstes. One is more vocal than the other. They generally only bark when someone comes down the driveway, but it's not a sure thing. They can someitmes bark to hear their own voice, or bark at the wind.
Bassets are very social dogs. That is why your little drooler barks outside. If it is a problem you can use a bark collar.
Your dog is doing what it was bred to do. Bark on the hunt. Whether they think a tree, another dog, a squirrel, or something you don't see if he is barking it means you have a good hunting dog. There are a lot of wonderful smells outside also. Long walks and training will usually help.
ok question. what is the "ultra sonic device" and "bark collar" that you speak of? my beagle howls and barks for who knows how long whenever i leave and i'm afraid it may begin to bother the neighbors if they can hear him. would you suggest something like this?