There is a sound (vibration) they can hear, so I'm not surprised. My horses always knew when it was off. My biggest concern with the electric fence (I'm NOT against it at all BTW) was we had to ride past it and with younger horses who could bolt it was a good possibility they could run YOU into the fence (almost happened once with BO).Are you serious? You have never had a smart horse. We've had horses (ponies are especially guilty) that KNOW when the fence is off or shorted out.