The RCI ICEPK is a small circuit that is placed in the door frame. It's used to eliminate strike overheating when strikes are used in continuous duty mode. After a time, it reduces the amount of current going to the strike while still allowing the strike to hold in the locked mode. It's particularly useful with compact electric strikes but works with all models. It wires in line with the electric strike.
Additional information available here: isicepk-r1119-pdf-data.pdf (dormakaba.com)