First used in the 16th century, key guns allowed a jailer to keep his weapon throughout the entire extremely vulnerable process of opening a cell door, thus never leaving him unprotected. Well, all except for the times when he's actually using the key/barrel end of the pistol to disengage the lock. That's right, key guns weren't just shaped like keys to throw people off or disguise their nature as pistols -- they're both functional keys and functional pistols (presumably so that if some uppity lock ever has the balls to stick on your watch, you can just shoot it off like a Renaissance Bruce Willis).
"Firepower is the key to victory. Did you get that? Was it too subtle?"
We get the feeling that not all implications were fully considered here. For example: Where do you keep your keys? If you said "dangerously close to my crotch," well, that's a weird way of saying "pocket," but no less technically correct. Plenty of people keep guns in their crotch area, sure, but what separates this is that the loop of the key (i.e., the place where you hold or pick it up) usually serves as the trigger for a key gun as well. So what are your Weaponized Door Access storage options? You could always hang it from one of those giant old-timey key rings that medieval jailers use in the movies. But then wouldn't you be suspending the pistol by its trigger and shooting yourself in the thigh with every jangle? Shit, we give up: If you have a convenient way to handle this thing without turning your own legs into gunshot-wound pie, speak up, because we're drawing a blank (unlike that unstable key gun pointed at your crotch).
This one had to be lit with a cigar, because any cigarless man in the 1850s deserved to die.