Has anyone see this or ever used it and what do you think of it?

i think it sounds pretty cool...it seems small enough that a dog wouldn't even know it was there, especially if you had a large breed dog. it would be a good aid in helping you determine if your dog is responding to training. hard to tell what the dog is doing when you're not around, isn't it? i have a couple neighbours who could use it...their dog barks all day & night...