Long before prison guards started carrying tasers, tear gas, and other non-lethal deterrents, they apparently relied on these cell door keys that also functioned as tiny one-shot pistols. They probably weren't lethal, but there's no doubt they packed enough of a punch to make an inmate very uncomfortable if they tried anything while a guard was unlocking their cell.
It remains to be seen how effective the weapons really were, particularly if they were used as actual keys (highly unlikely) but at the least they're definitely impressive feats of engineering and miniaturization, even to this day. [WonderHowTo via Boing Boing]
Images by WonderHowTo