I have the worst yapper I have ever known in a 4.5 lb Papillon. Really, you wouldn't believe the enthusiastic shrill barking that she is capable of. Shock collars are too strong for such a small dog, sonic controllers did not phase her, and the citronella collars didn't function. This has worked. She tries to bark, but only a few times and in a quieter tone, clever girl that she is. The only reason it was less than 5 stars is the collar loosens. I looped it back through the buckles and we'll see if that works. I want to thank my neighbors for not started a war with me; they would have had just cause to.