Personal alarms are one of the fastest growing solutions in self-defense because an attacker's worst enemy is attention. Personal alarms are legal to carry in all 50 states (even on airplanes) and are a very safe method of self-defense. They require no training or skill to operate, and can be used by anyone regardless of age or physical ability. Victims are often too traumatized to shout for help in unfamiliar and dangerous situations, increasing their vulnerability. Criminals do not like to draw attention, and will likely run off when they realize the alarm cannot be easily silenced.
The Mace Brand Personal Alarm Keychain emits a 130dB shriek.