This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
A very neat window lock can be made of sheet steel, 1/2in. wide. One piece, shaped like a saw tooth, is fastened to the sash, and the other, which is bent to form a catch over the tooth projection and ends in a curved top for a finger hold, is attached to the window casing. The illustration clearly shows how the lock is attached. - Contributed by Lee B. Green, Cleveland, O.