Abstract: A personal alert safety system (PASS) of the type carried by firefighters, rescuers, and the like. The unit attaches to the firefighters shoulder harness and is characterized by its ability to indicate audibly temperature changes in 100.degree. F. increments within the hazardous environment, as well as lack of motion by the firefighter. The activating circuit includes a horn alarm signalling both temperature changes and lack of motion, such that both the firefighter, as well as his colleagues, may be audibly apprised.