Don't feel bad, I wouldn't know what they are either if I hadn't been desperately looking for a way of controlling Gemma's wild barking at inconvenient times. It's a nylon collar with a little battery operated gizmo on it. When the dog barks, it instantly shoots a spray of citronella up underneath the dog's muzzle. The dog is startled by the spray and the unfamiliar odor, and, after making the connection between it and the barking, theoretically decides that it's better not to bark. The interesting thing is that, while dogs apparently dislike the lemony scent, humans think it's great! (It makes your house smell as if you've just been cleaning!)