Easy to install! Can also be mounted on patterned glass. The ALSOK mark will give up intrusion. This auxiliary lock can be installed inside to your home sliding door aluminum sash windows. The auxiliary lock is a great way to extend the criminal operations when breaking the glass (the way you took the glass near the crescent lock and insert your hands to open it). It can be applied directly to the glass surface with adhesive sticker, easy to install. There are 2 locking boards and only 1 sheet can be locked when the window is opened several centimeters for ventilation. From the outside, you can see the "ALSOK mark" printed on the adhesive side of the auxiliary lock, so you can expect crime prevention. Cannot be used with frosted glass. ·This product does not completely prevent intrusion. ·Please note that the color of the product may appear different from the actual product depending on the monitor used. ·There may be cases where there are differences in items that are not available in Tokyu Hands Stores. Please check with each store prior to handling instructions.