A window security device has a support rod capable of securely contacting an upper window frame and a lower window frame. The device has two horizontal arms extending from away from the support rod terminating in thin blades capable of sliding between a first stationary window and a second sliding window sash. The device prevents unwanted tampering with the device by children located on the inside of the window as well as burglars located on the exterior of the window and to be easily removed in the event of a fire. The length of the device's blade can be adjusted allow a window to safely remain open a specified distance, and the device's arms can be adjusted to fit many different widths of windows. When the blades are disposed between the windows, the window is slid open and contacts the window stop, located at the end of the horizontal arms.