A safer and perhaps more effective alternative to brass knuckles. It's usually a lightweight aluminum stick no more than 6 inches long that you hold in your fist. You strike your assailant using a backfist jab motion in a pressure point to pretty much stun them. Legal in all 50 states and can fit on your keychain if you get the right type.
An ex-girlfriend of mine got some drunk guys at a party together and told them to kick my ass. All five of them confronted me outside the back porch and I took out my kubotan and struck the main guy in the temple with a kubotan. The rest of the people freaked out and left.