The answer
Sometimes there were two small windows to either side of each door of the iconostasis, cut about one and a half meters above the floor. These were used during time of persecution, through which two deacons would watch the doors of the church from inside the sanctuary. In the case of an attack, they would alert the priest, who then hid the holy sacrifice, put out the candles and tore away the altar coverings so that they would not be used for non-sacred matters.
Fr. Tadros Yacoub Malaty