Tracking tripod for video camera?

I recently heard fourth-hand about a device someone was using to get a video camera to pan around and track them while they were practicing. Apparently the device involved some kind of small transmitter that one of the dancers would wear. Does anyone here know of such a thing?

I've seen one used but don't know where it came from. It had a Tx the man would wear on his belt--looked like a pager or something--and a Rx on the camera.