A window is positioned within a window casing and means are provided for rotatably connecting the window to the casing. A security apparatus includes a pair of rod holding brackets mounted on the casing on opposite sides of the window on an axis spaced from and substantially parallel to the rotational axis, each of the brackets having notch-like means for receiving and holding the end of a rod. An elongated rod is supported by the brackets and a permanent magnet is provided at one end of the rod to co-act with a magnetically operable switch attached to one of the brackets, the switch being connected to an alarm. When the window is closed the rod is positioned and held by the brackets and the permanent magnet causes the switch to have a first condition. The rod prevents the window from being moved from the closed position to the open position. If the rod is removed from the brackets, then the movement of the magnet away from the switch causes a change in condition of the switch to actuate the alarm.