Two shots like a derringer. These types of guns are for easy concealment and last ditch self-defense when shit goes south. Usually just showing a gun to an attacker is enough, but one or two shots will usually get you enough time to flee.
Umm... There are already lots and lots of this type of device already on the market, made by many manufacturers, and in the hands of law-abiding citizens, so... Yeah, not quite.
"Sure, just let me get my phone.."
*bang*
"Shit. That was not the phone"
YOU ARE TRYING TO KILL RATS WITH RATS