I was really hoping I had found something that would finally work to kill my dogs fleas. I have tried topical with no results and decided to do rit this collar. Its been almost 3 days and my dogs still have fleas and still scratching like crazy. I had to actually take off one dog b cause she got a rash from the collar. Looks like I will have to go to the vet and get a oral prescription pill since those always worked in my the past but not easy to administer. Seems like this product works great for some people but I was not one of those lucky ones.