Back in the good old days, turnkeys and jailers in prison did not walk around weapon free like they do in modern prisons. Opening the cell door was usually a two man job, and mischief from the inmates could often be expected at such moments. One of the solutions they employed was to have the key itself work as a gun. The tiny gun wouldn’t do huge damage, but it would get them enough time to thwart plans of the imprisoned.
Via WonderHowTo, BoingBoing