A personal alarm is a small hand-held electronic device with the functionality to emit a loud siren-like alarming sound. It is activated either by a button, or a tag that, when pulled, sets the siren off.
It is used to attract attention in order to scare off an assailant. The sound emitted can also have the effect of distracting, disorienting, or surprising the assailant.
The volume varies from model to model, with some models having 130 decibels. Some personal alarms are also outfitted with an LED light for normal lighting purposes or to help deter an assailant.
Some personal safety apps emit a loud intermittent “shrill whistle”, in the manner of a personal alarm.