Abstract: A device for selectively preventing more than a desired opening of a metal frame and sash window having at least one sash mounted for relative sliding movement in overlapping relation to another sash to open and close the window. A metal keeper is mounted in the side rail of the upper window of a double-hung sash and a bolt or pin extends removably therefrom for intercepting and halting opening of the window, thus permitting the window to be opened slightly for ventilation but not far enough to allow unlawful entrance. A spring-biased finger detent, extending into the bolt or pin receiving opening of the keeper, engages a circumferential groove on the bolt or pin for inhibiting accidental removal from the keeper. In another form of the invention, the bolt is screwed into the keeper.