A simple installation of a Window Lock (Sash Jammer) can make a major difference in the way your home is protected from intruders and burglars! A sash jammer is an additional security device that can be fitted to uPVC windows and rebated doors. It can also be used as window / door child safety device. The sash jammer is simply screwed to the window or door, the arm of the sash jammer is turned to catch the sash / or the frame (depending on how the window or door opens) which stops is from opening.