There are several types of locks that can be installed on sash windows. Here are a few of the common ones: Sash fasteners: These are the primary lock for a sash window. They’re usually quite robust and are designed to firmly hold the top and bottom sashes together when the window is closed. Some sash fasteners are even lockable with a key for added security. Sash stops or sash jammers: These clever devices can stop the window from being opened beyond a certain point. They are great if you want to let in some air but also want to keep your window secure. Dual-screw locks: These offer a higher level of security by firmly connecting the two sashes together. This makes it much harder for anyone to force the window open from the outside. Key-operated locks: These are a solid choice for extra security. They are placed on the meeting rail, and a bolt enters a keep in the other sash when turned, securing the window. It’s important to remember that locks are just one part of window security. The quality of the glass and the frame also play a significant role. Using reinforced or laminated glass can make your sash windows even more secure. And always remember – the best advice will come from a professional window installer, who can take into account all the specifics of your home and your individual needs.