This auxiliary lock can be easily installed by inserting it into the sash groove and turning the knob. It prevents intrusion from windows and is ideal for crime prevention measures. Recommended for those worried about burglars and thieves, women living alone, and households with small children or pets. We recommend installing two, one at the top and one at the bottom, to enhance the crime prevention effect. *This product does not completely guarantee theft prevention. Please be aware of this. 【Ventilate while taking crime prevention measures】 "I want to ventilate, but I'm worried about security..." This solves that problem! You can lock it even when it's slightly open, so you can use it with peace of mind while changing the air. Safe for households with children who might open the lock. Also convenient for intermediate stops on windows where air conditioners and ventilation fans are installed. It can also be used in kitchens, bathrooms, toilets, living rooms, etc. *The crime prevention effect is slightly reduced when used with the window open. 【Impact-resistant and durable material】 Made of die-cast steel + rubber, it has excellent impact resistance and durability. The large knob allows for secure tightening. Easy to operate and can be firmly fixed. Recommended for those with a high awareness of crime prevention as a way to buy time against intrusion. *Does not guarantee complete theft prevention. 【Easy installation, no construction required】 Compatible opening width: 2.8cm to 4.2cm No tools or construction required. Simply insert it into the sash groove and turn the knob to secure it firmly. Please install it so that it adheres to the window frame. *Please be sure to check the fixed state. *Not compatible with all sashes. Please check the size before purchasing. 【How to use/Applications】 ● Usage location: Compatible with both the top and bottom of the window frame ● Material: High-quality die-cast steel + rubber (scratch-resistant and long-lasting) ● Applications: Preventing windows from opening too much, preventing mischief, and providing crime prevention assistance ● Also effective as a countermeasure against rain, wind, and water spills #MercariHalloween