Windows often come under attack. There is now an effective solution for double windows: the VdS-approved ABUS DFS 95 double window lock.
A gap of 18-35 mm between the two halves of the window is a prerequisite. The claw action of the solid double swivel bolt secures both halves of the window simultaneously. As a result, the windows are particularly difficult to lever open: a force in excess of one tonne can be applied to the double window lock. The convenient click mechanism means that the lock can be secured without a key. From inside, you can see at a glance whether the window is locked or not.