Whether you're the one being made crazy by your dog's barking or your neighbors are complaining, something has to be done if your dog is making too much of a racket. Sonic devices can help by immediately letting your dog know that he's done something wrong.
How It Works
Sonic devices take advantage of the fact that dogs can hear certain high tones and pitches that humans can't. Each time your dog barks, the device plays a tone that is irritating to him, but can't be heard by you. Before too long, your dog associates the tone with his barking and learns it is unpleasant for him if he barks too much.
Collar
Sonic devices attached to collars have the advantage of being conveniently attached to your dog. No matter where he goes, the collar can remind him of the consequences of barking. On the other hand, these collars are expensive and can easily be ruined, especially in a home with two dogs, where one might chew on the other's collar.
Stationary Unit
If your dog is contained in a certain room or in a kennel, a stationary unit can be placed near your dog, but out of his reach. Just like the collar, the unit puts out a high-pitched sound whenever he barks. Unlike the collar, though, it can be put in a safe place where your dog can't destroy it. The downside is that the further your dog gets away from the device, the less effective it is.
Considerations
Sonic devices are not meant to be used as a stand-alone training tool, but are often used that way, limiting their effectiveness. Sonic anti-bark devices are much more successful when used in conjunction with a training program. The devices are also not meant to be used all of the time. Use them only when the problem is occurring, such as in the evening when your dog is outside and so are the neighbors. Otherwise, your dog could learn to ignore the sounds and continue barking despite the device.