This unique Window Warden allows windows to open up to a maximum of 4" but prevents them from opening further. This innovative safety device lets you enjoy fresh air safely and is great for children and adults who need supervision. The quick-release button allows for easy removal by adults for whatever reason: full-window access, cleaning, emergency situation. This window opening limiting device works on most double hung windows, sliding windows and sliding doors and is NOT intended for casement, awning, hopper-type windows, or windows with deep, open channels.