Virtual Fences

"The Ear-a-round consists of a small, light box that sits on top of a cow’s head, and a pair of earpieces made of fabric and plastic. The box contains a computer chip, a GPS tracking device and a transceiver that enables it to be programmed remotely. The earpieces serve both to keep the box upright and to supply command signals—either sonic or electric—to the animal wearing the device. For maximum working lifetime, the whole thing is powered by lithium-ion batteries that are topped up by solar cells."

Economist