Passive acoustic monitoring of scuba divers is a promising way to ensure the safety of recreational divers and prevent waterside intrusion by terrorists. It is shown experimentally that the low-frequency underwater respiratory-associated noise of an open-circuit scuba diver can be used successfully to monitor the respiratory rate at distances of up to 100 m. Respiratory-associated noise in the frequency band of 30-1200 Hz provides the possibility of localizing an open-circuit scuba diver in a noisy shallow-water area by using two pairs of hydrophones at distances of up to 220 m and with a predominant discrepancy of no more than 10 m in comparison with Global Positioning System data.