Abstract: An expandable intrusion detection screen for use with an audible electronic alarm has first and second screen panels slidably movable in parallel relation to each other to be expandable to fit within different sized window openings. The alarm is mechanically mounted and retained within an internal peripheral channel in the frame of one of the screen panels and has an intrusion detector extending outward through the frame of the screen panel for detecting the separation of the screen panel from any part of the window against which the detector is placed when positioned in a window opening.