An obstruction detection apparatus is provided for use in closing a power driven vent, such as a window (1035), that is located in an opening (1042). The vent includes a first closing edge that moves as the vent is closed and the opening includes a second closing edge that is contacted by the first closing edge when the vent is in a fully closed position. The apparatus includes a detector (1060) configured to detect an obstruction at all points along the second closing edge without requiring contact between the obstruction and the vent and to deliver a detection signal when an obstruction is detected. A controller is connected to the detector for receiving the detection signal and delivering a corresponding alarm signal.