Abstract: A new and improved security device for controlling window blinds by automatically periodically lifting and lowering a single slat of a conventional venetian blind or mini blind set to simulate human activity to an observer located outside the window. The security device for controlling window blinds comprises a motor-driven pull-cord clipedly connected to a slat of the window blind set, a motor having a motor controller whereby the frequency and duration of the slat movement is established, and a fairlead wherethrough the pull-cord is routed from the window blind slat to the drive motor.