upper sash when the block is mounded on the window upper sash frame the push button switch is pointed downward to intercept any effort to raise the lower sash any further than a few inches in the event that the upper sash is of moveable design the block is carried down with a lowering sash movement that restricts and limits the possible distance movement of either or both upper and lower sash i e the mathematical sum of the two opening spaces is a fixed sum adhesive such as is found on double sided adhesive tape holds the block in position on vinyl coated aluminum window frames with very good service quality and it tenaciously resists removal by hand action wooden window frames of a lesser polish surface may give mixed results one can add a polished surface plate to the wood such a plate can be attached with glue e g epoxy if the attached plate is steel ferromagnetic material the steel provides a convenient mounting and release feature with the mounting of an intermediate ferromagnetic layer the safety block can be attached to glass to aluminum to wood with ease a sixteenth inch thick or thinner steel plate is adequate for holding fast.