Personal alert safety systems (PASS) are devices used by emergency responders to indicate distress or a need for assistance in extreme environments. These systems use features such as strobe lights, audible alarms, and radio communications to help locate personnel in the field. They are most commonly worn by firefighters in immediately dangerous to life and health (IDLH) scenarios, and are considered an essential piece of safety equipment. As such, they are frequently linked to or worn on the self-contained breathing apparatus. Modern models often register user motions via a ball bearing or infrared accelerometer, and when inactivity is registered it automatically signals an alarm. Older models require the wearer to manually signal a distress. These battery-powered devices emit an audible alarm of at least 95 decibels. When the alarm is triggered, it initiates a rescue initiative on behalf of other first responders.
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