Abstract: A system for monitoring the security of one or more persons in a waterside environment and for providing a failure proof indication of when such person falls into the water. The system includes a portable transmitter worn about the body of the person whose security is being monitored in a location which insures its submergence when the person falls into the water. Transmissions from the portable unit, which may be either time shared or the result of an interrogation from a base station, are monitored at a base station. Continuous presence of the transmitted signal from each portable unit inhibits an alarm condition at the base station, but if the transmitted signal is not received, or is not received for a predetermined time period, the alarm condition is activated and the portable unit not transmitting is identified. The lack of a transmitted signal indicates a "man overboard" condition resulting from the transmitter being immersed in the water and transmissions thus blocked.