PASS device

A PASS device (Personal Alert Safety System) also known as a distress signal unit (DSU) or ADSU (Automatic Distress Signal Unit), is a personal safety device used primarily by firefighters entering a hazardous (IDLH) environment such as a burning building. The PASS device sounds a loud (95 decibel) audible alert to notify others in the area that the firefighter is in distress. On a fireground, the sound of an activated PASS device indicates a true emergency and results in an immediate response to rescue the firefighter(s) in distress. In the United States, the National Fire Protection Association sets standards for PASS devices in NFPA 1982.

The PASS device is normally used in conjunction with breathing apparatus; it is a small, battery powered device attached to the self-contained breathing apparatus (SCBA) harness which enables the firefighter to summon help by activating a loud, piercing electronic bleeper.

Early models were only able to be activated manually; more recent PASS devices automatically activate if the device does not detect motion for 30 seconds, so that the alert will sound if the firefighter is seriously injured or otherwise incapacitated. Some devices use a ball bearing on a track to sense firefighter movement and others use an infrared beam against a mirror mounted on a spring. When activating for a lack of motion, the PASS device will typically emit a few seconds of a muted warning that activation is about to occur, so that a firefighter who has simply been motionless for a time but is otherwise safe will be able to move slightly and thus reset the activation timer before a false activation occurs. The PASS device can also be activated manually in an emergency, such as when a firefighter is lost or trapped.