A rotatable security bar mechanism permanently attached to the frame of a slidable panel such as a patio door or window, capable of being operated without interfering with the normal operation of the panel or window, is disclosed. The pivoting security bar assembly includes a single bar section having generally rectangular dimensions and which are disposed to interfere with the direction of travel of a slidable panel or door in its normal operating direction. The Security bar rotates about hinges alternatively in an open and closed position to cover the slidable track area of the slidable or moveable panel member. When the bar is in the locked position, it covers slidable track members utilizing the shape, design, and trim levels which are similar to the design trim of the slidable panel or window units color and design, such as to be unnoticeable. The present disclosure also provides the application of the security bar mechanism to a double hung, slidable window design to provide enhanced security by providing a blocking means to the operation of the window. Also disclosed are certain and various enhancement of the locking mechanism to provide for additional security for the rotating security bar. The present invention also allows for ease of use by handicapped or sightless individuals, as well as individuals perhaps confined to a wheelchair.