Some places a firearm of any sort is not legal. Knife, a bar of soap in a sock.
After 9/11, when they stopped allowing me onboard commercial flights with my lockblade knife, I started carrying a three inch tall, solid brass, owl statue with me in my carry-on luggage. I wrapped it up in a rugged cloth dinner napkin, and put it in a small gift box, as if I'm taking it as a gift to someone I'm visiting.
Pull that thing out, put it in the center of the dinner napkin, fold the rest back, and it's a Medieval mace.
