Works for 1 dog not for a pack......

I purchased this to stop my daughter’s beagles from barking all night. At first, when just 1 barked it worked. However; when you get 7 barking at one time you just as well forget it. I had it on the highest setting and they still out-barked it. I am not at a total loss. My Chihuahua, Moose, knows what it is and I don’t even have to turn it on. All I do is show it to him, that's it, he stops barking and lays back down. I do wish they would change the picture in the advertisesment. It's awful!