It's an electric fence. He is only on it at my parents farm. They are normally not as bulky as this one but he needed the "stubborn dog" collar. It beeps and vibrates before he gets zapped. He has only got zapped once with this collar it pretty much dropped him. Won't go near the horses, the road , or my moms vegetable garden anymore. With the smaller collar he kept just crossing the line. It lets him run on 5 acres with the oter dogs yet keeps him outa the manure pile, road, ect. Ect. He learned t in about a week.